Journal o f Cluster Science, Vol. 5, No. 3, 1994
Synthesis and Structure of Complexes Formed in the Reaction Between Dicobalt Octacarbonyl and Tetramethyl-Biphosphine Disulfide Giuliana Gervasio, ~ Fabrizio Musso, I Sändor Vastag, -~ György Bor, 2 Gäbor Szaiontai, 3 and Läszló Markó 4 Received Jam«ary 12. 1994
Co2(CO)s and Me2P(S)P(S)Me2 react to form the two cluster complexes: Co4(CO)!)S(PMe2) 2 (1) and Co3(CO)TS(SPMe,) (2). The structure of 1 and of the disubstituted triphenyl phosphine derivative of 2, Co3(CO)5(PPh3)2S (SPMe:} (2a) were detemained. Compound 1 contains a quasi-planar rhomboidal Co4 cluster formed by two Co 3 isosceles triangtes sharing a C o - C o edge. One triangle is capped by a sulfur atom, the other triangle has two edgebridging PMe, moieties. Electron counting gives 64 electrons corresponding to a planar system; the distribution of long C o - C o distances, in particular in the triangle bearing PMe 2 bridges, suggests that the excess electrons are located on C o - C o antibonding orbitals. Compound 2a contains a Co3S cluster with one side bridged by a SPMe 2 unit forming a four-membered Co2SP ring, The substitution of two CO groups with two PPh 3 causes a large deformation of the cluster C o - C o bonds cis to these two phosphorus atoms. Crystal data for 1, space group P1, a=9.728(2)A, b=10.288(2) A, c=11.860(3)A, 0¢= 86.41(2) °, f l = 76.20(2) «, ),= 80.37(5) ~~, Z = 2 , 5300 reflections, R = 0.0398; for 2a, space group PI, a=9.78(3) A, b = 13.05(4) A, c = 18.28(6) Ä, c¢= 93.23(3) '~, fl = 99.17(2) °, 7,= 97.26(6) , Z = 2, 2976 reflections, R = 0.0579.
KEY WORDS: Sulfur-containing
cobalt carbonyl biphosphine disulfide; dicobalt octacarbonyl.
clusters;
tetramethyl
Dipartimento di Chimica Inorganica, Chimica Fisica e Chimica dei Materiali, University of Torino, 1-10125 Torino, Italy. 2 Institute of Organic Chemistry, University of Veszprém, H-8200 Veszprém, Hungary. Central Laboratory, University of Veszprém, H-8200 Veszpröm, Hungary. « Research Group Ihr Petrochemistry of the Hungarian Academy of Sciences, H-8200 Veszpröm, Hungary. 401 1040-7278/940900-0401507.00/0~~ 1994 Plenum PublishingCorporation
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INTRODUCTION The reaction between Co2(CO)s and M % P ( S ) P ( S ) P M e 2 was first described in 1972 and the formation of two clusters, C o 4 ( C O ) g S ( P M e 2 ) 2 (1) and Co~(CO):S2(PMe 2) (2) as main products was reported [1]. Several structures were suggested by the authors for these complexes based on mass spectrometric results but no X-ray diffraction analysis has been carried out and the available information was not sufficient for an unambiguous structure determination. Motivated by our long-lasting interest m the chemistry and structure of sulfur-containmg cobalt carbonyl complexes we repeated the synthesis of the two complexes and determined their structures. EXPERIMENTAL
The preparative procedure was essentially identical with that described by Natile and co-workers [1]; 342mg (1 mmol) Co2(CO)s and 186mg (1 mmol) Me4P2S2 were dissolved in 20tal dichloromethane and the reaction mixture stirred under CO at l atm for 3 days. As shown by IR spectroscopy at the end of the reaction no more Co2(C0)8 was present in the product. The dichloromethane solution was evaporated to dryness hl vacuo, the solid residue dissolved in 10ml hexane and cooled overnight to - 1 5 ° C . The dark green crystals of 1 were filtered oft" and recrystallized from hexane. Yield 100 mg (0.156 mmol), 31.2%, based on cobalt. Elementary analysis and infrared spectroscopy proved that the compound was identical with that described in Rel. 1. From the mother liquor of the first filtration, complex 2 could be separated after concentrating the solution by partial evaporation h,~ vacuo and chilling to - 7 8 ° C but the crystals obtained in this way were not suitable for X-ray diffraction. Therefore the triphenyl phosphine derivative 2a was prepared in the way that to the same mother liquor 262 mg (1 mmol) triphenyl phosphine was added and the solution was chilled to - 1 5 ° C . The dark brown crystals of 2a were filtered oft" and recrystallized from acetonitrile. The complex crystallizes with one molecule of M e C N (Found: C, 53.57; Co, 17.75, 17.50; N, 1.65; P, 9.35, 9.20; S, 6.88; calc. for C45H39Co3NO5P3S2; C. 53.64; Co, 17.66; N, 1.39; P, 9.22; S, 6.36%). Yield 90 mg (0.089 mmol), 13.4% based on cobalt. Infrared spectrum in nu]ol: 2028s, 1986vs, 1958m, 1937m, 1917mcm -~ ( C - O stretching region), 2242vw cm ~ ( C - N stretching ). Ci3,stallographic Analysis. The crystal data for complexes 1 and 2a are collected in Table I; the parameters of collection and of refinement of the
403
Clusters Formed from Coz(CO)s and Me4P2S 2 Table i. Crystal Data for Co4(CO)gS(PMe2) 2 (Complex 1) and Ihr Co3(CO)sS(PPh3)2(SPMe2) (Complex 2a)
Complex 1 Empirical fonnula Color; habit Crystal size (mm) Crystal system Space group Unit cell dimensions
Volume Z Formula weight Density(calc,) Absorption coefficient F(000)
Complex 2a
Ct3HI2Co4OgP2S
C.~5H39C03 NO s P3S 2
Dark-green, prism 0.70 × 0.60 × 0.20 Triclinic P] a = 9.728(2) A b = 10.288(2) A «= 11.860(3) A 0¢= 86.41(2)° B= 76.20(2)~' ),= 80.37(5)" 1136.1(4) A3 2 641.9 1.876 Mg/ms 3.141 mm ~ 632
Dark-red, lamina 0.40 × 0.20 × 0.08 Triclinic Pi a = 9.78(3) A b = 13.05(4) A «= 18.28(6) A « = 93.23(3)~~ fl = 99.17(2)" ), = 97.26(6)«~' 2278(13) A3 2 1004.6 1.464 Mg/ms 1.321 mm i 1022
data are listed in Table II. F o r the a b s o r p t i o n correction the method of Ref. 2 was applied. The final fractional coordinates a n d the equivalent isotropic displacements are in Tables III and IV (for the atoms isotropically refined U(eq) is equivalent to U(iso)). The large difference between the final results of the two complexes are due to the bettet quality of the crystal of complex 1. F o r this reason an anisotropic refinement was applied to all n o n h y d r o g e n atoms for complex 1; on the final F o u r i e r difference maps hydrogens of the methyl groups were located a n d then refined riding on the c o r r e s p o n d i n g c a r b o n atoms. F o r complex 2a only the Co, P, S, and C O groups were anisotropically refined, a n d the hydrogen positions were calculated. In complex 2a a molecule of solvent ( C H 3 C N ) with very high thermal parameters was found. The data were collected at room temperature on a Siemens P4 diffractometer, with 2 ( M o K ~ ) = 0 . 0 7 1 0 7 3 A, graphite m o n o c h r o m a t i z e d . The system used for solution a n d refinement was S H E L X T L IRIS. The structures were solved by direct methods and the q u a n t i t y minimized with the full-matrix least-squares was Xw(F,,-F,.) 2.
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Clusters Formed from C02(CO) ~ and Me4P2S 2 Table III.
Co(l) Co(2) Co(3) Co(4) S C(II) 0(1l) C(12) 0(12) C(21) 0(21) C(22) 0(22) C(31) 0(31) C(32) 0(32) C(41) 0(41) C(42) 0(42) C(43) 0(43) C(I) C(2) C(3) C(4) P(I) P(2)
405
Atomic Coordinates ( × ]04) and Equivalent Isotropic Displacement Coefficients (A2 × 103) for Co4(CO)gS(PMe2)2u x
y
:
U(eq)
4247(1) 1629(1) 3888(1) 6380(1) 5082(1) 3525(4) 3044(4) 5342(4) 6029(3) 282(4) -658(3) 1423(4) 1154(4) 3271(4) 2902(4) 4448(4) 4770(4) 6174(4) 6044(4) 7320(4) 7948(3) 7833(4) 8761(4) 612(4) 2066(5) 1607(4) 2964(5) 1842(t) 2472(I)
1359(1) 2674(1) 3934(1) 2583(1 2612(1 1205(4 1086(4 -200(3 -1197(3 2672(3 2647(3 2676(4 2669(4 4175(4) 4355(4) 5464(3) 6457(3) 2467(4) 2404(4) 3983(4) 4835(3) 1249(4) 444(4) 5889(4) 5625(4) -536(3) -294(4) 4704(1) 629(1)
2786(t) 2244(1) 2703(1) 2627(1) 1351(1) 4326(3) 5282(3) 2482(3) 2286(3) 3525(3) 4310(3) 823(3) -57(3) 4234(3) 5196(3) 2235(4) 1920(4) 4169(4) 5150(3) 2272(3) 2074(3) 2124(4) 1798(4) 3176(4) 817(4) 3311(4) 946(4) 2197(1) 2279(1)
35(1) 35(1) 35(1) 41(1) 37(1) 54(1) 93(2) 52(1) 81(1) 47(1) 77(1) 56(1) 97(2) 55(1) 94(2) 59(1) 98(2) 58(1) 87(2) 49(1) 73(1) 64(2) 109(2) 66(2) 69(2) 63(2) 65(2) 39(1) 38(1)
" Equivalent isotropic U defined as one third of the trace of the orthogonalized Uo tensor.
DESCRIPTION OF THE STRUCTURES
Complex I, C o 4 ( C O ) g S ( P M e 2 ) 2. Figure 1 shows a view of the molecule with the atom-labeling scheme. Table V lists the more relevant distances and angles. Complex 1 is formed by a Co3S cluster with one side bridged by a Co(CO)2 unit; the two resulting isosceles triangles share the Co(1)-Co(3) bond and form a dihedral angle of 163.5 °. The triangle belonging to the Co3S cluster has two sides shorter (2.568(1)A av.) than Co(1 )-Co(3), the other triangle has two sides longer (2.886(1) A av.) than
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Gervasio et al.
Table lV,
Atomic Coordinates ( x lO4) and Equivalent Isotropic Displacement Coefficients (A2x I0 3} for C o 3 ( C O ) s S ( P P h 3 ) 2 { S P M e 2 ) `~ x
Co( 1) Co(2} Co(3) C(ll) O(11) C(21) O(21) C(22) 0(22) C(31} O(31) C(32) 0(32) S(I) S{2} P(l) P(2) P(3) C(l) C(2) C(3) C(4) C(5) C(6) C(7} C(8) C(9} C(10) C(IlA) C(12) C(13) C(14) C(15) C(16) C(17) C(18) C(19) C{20} C(21A} C(22A} C(23} C(24) C(25) C{26)
1628(2) 3481(2) 1911(2) 2687(12) 3395(9) 4450(13) 5241(9) 4586(14) 5427( 10} 3026(14) 3696(I 1} 1749(13) 1575(11) 1235(3) --449(3) --100(3) 980(3) 3984(3) --1605(11) --172(12) -117(1) - 1 0 9 0 1}
-- 2012 13) --1969 14) --1081 12) --t40 12) --66(I) 325 13) --458 13) --1653 13) --2049 13) -1265 13) 2461(1) 3025 13} 4296 14) 4915 14) 4357 14) 3140 12) 3188(I0} 3239(11) 2744(12) 2129(13) 2069(12) 2597(11)
y 8437(I) 8143(1) 9536(1) 9231(10) 9773(7) 7993(9) 7965(7) 9142(9) 9756(6) 10626(10) 11308(7) 9874(10) 10077(9) 7862(2) 9107(3) 9918(2) 7098(2) 6889(2) 9597(9) 11265(8) 5951(8) 6076(9) 5229(9) 4295(10) 4130(10) 4969(9) 7431(8) 8346(9) 8633(10) 8011(9) 7128(10) 6796(9) 6567(8) 6935(9) 6605(10) 5912(10) 5556(10) 5900(9) 6831(8) 7742(9) 7744(10) 6826(10) 5937(10) 5925(9)
z
U{eq)
2160(1) 3280(1) 3350(1) 1666(6) 1352(5) 2576(7) 2160(5) 3819(7) 4177(5) 3100(8) 2925(6) 4283(8) 4869(5) 3205(2) 1801(2) 2796(2) 1309(2) 3997(21 3237(6) 2644(7) 1524(6) 2000(6) 2140(7) 1799(7) 1333(7) I198(6) 444(6) 131(7) --503(7) -831(7) - 535(7) 110(7) 1016(6} 409(7) 277(7) 712(7) 1298(7) 1459(7) 4836(5) 5254(6) 5924(7) 6150(7) 5743(7) 5074(6)
33(I) 34(1) 38(1) 45(5) 75(4) 46(5) 68(4) 47(5) 72(4) 63(6) 98(5) 62(6) 102(5) 35(1) 50(1) 39(1) 37(1) 30(1) 56(4) 60(4) 40(3) 49(3) 60(4) 69(4) 61(4) 49(3) 38(3) 56(4) 66(4) 62(4) 62(4) 56(4) 40(3) 59(4) 71(4) 69(4) 71(4) 54(4) 32(3) 44(3) 56(4) 66(4) 57(4) 45(3)
407
Clusters Formed from Co2(CO) 8 and Me4P2S ~
Table IV. ( C o n t # m e d ) x
C(27) C(28) C(29) C(30) C(31A) C(32A) C(33) C(34) C(35) C(36) C(37) C(38) N(1) C(39) C(40)
5847(10) 6393(12) 7835(13) 8711(14) 8207(14) 6773(13) 3508(11) 2085(12) 1666(14) 2669(13) 4030(14) 4460(12) 3282(19) 3399(18) 3650(18)
y
z
6944(8) 6981(8) 7049(9) 7(/90(9) 7042(9) 6998(9) 5582(8) 5248(9) 4284(9) 3686(10) 3967(10) 4924(8) -1221(15) -345(16) 707(14)
4361(6) 5093(6) 5332(7) 4828(7) 4082(7) 3854(7) 3544(6) 3280(6) 2877(7) 2766(7) 3057(7) 3448(6) 8898(10) 9160(10) 9401(10)
U(eq)
33(3) 50(3) 65(4) 67(4) 66(4) 57(4) 33(3) 48(3) 62(4) 64(4) 63(4) 44(3) 169(7) 109(6) 114(6)
" Equivalent isotropic U defined as one third of the trace of the orthogonalized Uv tensor.
221
BOI211
Fig. i.
ORTEP view (50% probability) of complex 1, C04(CO),~S(PM%)2, atom-labeling scheine.
with the
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Gervasio et al.
Table V. Relevant Bond Lengths (A) and Angles (") for Complex 1 Co(l) Co(2) Co(l) Co(4} Co(I) C(ll) Co( 1)-P(2) Co(2)-C(21) Co(2)-P(I) Co(3) Co(4) Co(3)-C(31 ) Co( 3)- P( I ) Co(4)-C(41) Co(4)-C(43) C(12) 0(12) C(22) 0(22) C(32) 0(32) C(42) 0(42) C(I)-P(I) C(3) P(2) Co(2) Co( I ) Co(3) Co(3) Co(1)-Co(4) Co(3) Co(I)-C{ll) Co(2) Co(l) C(12) S Co(1)~C(12) S Co(1)-P(2) C(12)-Co(1) P(2) Co(l) Co(2)-C(21) Co(I) Co(2) C(22) C(21) Co(2) C(22) C(22)-Co(2)- P( 1) C(22)-Co(2) P(2) Co(l) Co(3)-Co{2) Co(2) Co(3) Co(4) Co( 2 ) Co( 3 ) C( 31 ) Co(2)-Co(3)-C(32) S Co(3)~-C(32) S Co(3) P(1) C(32)-Co(3) P(I) Co( 1)-Co(4) C(41) Co(3)-Co(4) C(42) C(41)-Co{4) C(42t S-Co(4) C(43) C(42)-Co(4)-C(43) Co(l) S-Co(4) Co(I)-C(I1) 0(11) Co(2) C(21 ) 0(211 Co(3) C(31) 0(31) Co(4) C(41 ) 0(41) Co(4) C(43)-0{43)
2.872(l) 2.567(1) 1.801{4) 2.212(I) 1.754(3) 2.129(1) 2.570(1) 1.790(4) 2.220( 1) 1.790(4) 1.814(4) 1,131(4) 1.136(6) 1.133(5) 1.132(5) 1.814(4) 1.818(4) 63.7( I ) 59.5(1) 96.0(I) 135.5(I) 104.2(1) 104.7(I) 9(t.211) 106.9(I) 119.5(I) 127.1(2) 94.9(I) 94.3(1) 62.5(1) 119.8(1) 100.9( 1) 131.9(2) 103.8( 1) 105,2(1) 87,9(1) 90.8(I) 94.8(I) 100.8(2) 102.0(2) 100.4(2) 72.5(1) 177.9(4) 174.9(4) 178.2{4) 179.4(4) 178.1 (4)
Co(l) Co(3) Co(l) S Co(1)-C(12) Co(2) Co(3) Co(2) C(22) Co(2) P(2) Co(3)~S Co(3) C(32) Co(4 ) S Co(4) C(42) C(II) 0(11) C(21) 0(21) C(31) 0(31} C(41) 0(41) C(43) 0(43) C(2) P(1) C(4) P(2) Co(2) Co( 1)--Co(4) Co(2) Co(1)-C{II) Co(4) C o ( I ) - C ( I I ) Co(4)-Co(I)-C(12) C(ll) Co(1)-C(12) C(II) Co(I)-P(2) Co(1)-Co(2)-Co(3) Co(3)-Co(2)-C(21) Co(3) Co(2) C(22) C(21)-Co(2)-P(1) C(21) Co(2)-P(2) P(1)-Co(2)-P(2) Co(I) Co(3) Co(4) Co(l) Co(3) C(31) Co(4 )- Co( 3 ) C( 31 ) Co(4) Co(3) C(32) C(31 )- Co(3)-C(32) C{31)-Co(3)-P(11 Co(l) Co(4) Co(3) Co(3)-Co(4)-C(41 ) S-Co(4)-C(42) Co(I) Co(4)-C(43) C(41 )-Co(4) C(43) Co( l )-S-Co(3) Co(3) S Co(4) Co(l) C(12) 0(12) Co(2) C(22) 0(22) Co(3) C(32)-0(32) Co(4)-C(42) 0(42} Co(2) P(I)-Co(3)
2.612(I) 2.153(1) 1.776(3) 2.901(I) 1.743(4) 2.128(I) 2.150(I) 1.765(4) 2.186( 1) 1.808(4) 1.126(5) 1.141(4) 1.128(5) 1.139(5) 1,129(5) 1,824(4) 1.818(4) 121.0( I ) 95.9(1) 104.0(I) 93.9(1) 101.7(2) 95.2(2) 53.8(1) 108.2(1) 118.9(I) 98.1(I) 97.1(1) 152.2(1) 59.4(1) 97.0(1) 100.2( 1) 97.6(I) 100.8(2) 98.1(I) 61.1(1) 95.2(I) 106.4(1) 99.2(I) 102,5(2) 74.8(1) 72.7(1) 179.4(4) 173.4(4) 177.8(4) 177.2(4) 83.6(1)
Clusters Formed from Co~(CO)8 and Me4P2S 2 Table V.
Co(2) P(1) C(1) Co(2)- P( I )-C(2) C(1)-P(1) C(2) Co(l) P(2) C(3) Co( 1)- P(2)-C(4) C(3) P(2)-C(4)
122.6(1) 119.7(I} 101.8(2) 114.6(2) 115.7(2) 101.5(2)
409
(Cbntim¢ed) Co(3) P(I) C(I) Co(3)-P( 1)-C(2) Co(1)-P(2).-Co(2) Co(2) P(2) C(3) Co(2)- P(2)- C(4)
115,3(2) 113.9(2) 82.9(1) 122.6(I) 119.9(I )
Co(1)-Co(3). These last two bonds are bridged by PMe2 units and, together with the C o ( 1 ) - C o ( 3 ) bond are longer than the C o - C o distances usually found in diamagnetic Co3S clusters [3]. The cobalt atoms Co(I), Co(2), and Co(3) are linked to two CO ligands whereas the Co(4) atom is associated to three CO ligands. The phosphorus atoms of the bridges are 0.1 Ä out of the Co(1)Co(2)Co(3) plane on the same side as the sulfur atom; the bridges are asymmetrical with the P ( n ) - C o ( 2 ) distances being shorter (2.128(1)Ä av.) than the P ( n ) - C o ( 1 , 3) distances (2.216(1)A av.). The C o - P distances are of the same order or shorter than the C o - P P h 3 distances in complex 2a. It should be mentioned here that ruthenium carbonyl clusters with similar structures and bonding characteristics, R u 4 ( C O ) I 3 ( P R 2 ) 2 , have been synthesized and studied recently [4]. Within the Co3S cluster the C o ( 4 ) - S distance is longer than the other two, as already fbund in all other similar complexes where sufficiently accurate data have been reported [3, 5-8]. As in the corresponding R u 4 complexes the four methyl groups bonded to phosphorus are eclipsed with the carbonyls of Co(2).
Complex 2a, Co.~(CO)5(PPh~)zS(SPMe:). Figure 2 shows a view of the asymmetric complex 2a with the atom-labeling scheme. Table VI shows the more relevant distances and angles. The framework of 2a is a Co3S trigonal pyramid with one C o - C o side bridged, equatorially with respect to the Co3 plane, by a SPMe 2 group. This ligand gives rise to a four-membered ring similar to those found in the complexes [C03(CO)7S]2S 2 [5], Co3(CO)7S(MeCNC6HIm) [6], Co~(CO)7S (CSNMe2) [7], Co3(CO)TS(NHCMeS) [8], and Co3(CO)gCSCSCo3S(CO) 7 [9]. The atoms C o ( 1 ) - C o ( 3 ) - S ( 2 ) - P ( 1 ) of the ring lie on a plane with an average deviation from planarity of 0.014 A; this plane forms an angle of 13 ° with the Co 3 plane. Co(3) links two carbonyls (eq, ax), Co(l) links an axial carbonyl and an equatorial PPh3 group, while Co(2) bonds two carbonyls and one PPh3 group. Examining the coordination of this last Co atom we see a deviation
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~( ~""~~~P(00(2} I(21) ~
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Fig. 2. ORTEP view (50% probability) of complex 2a, Co3(CO)vS(SPMe~), with the atom-labeling scheme.
with respect to the other similar structures where no substitution [e.g., 5-8] or only a mono-substitution occurs [ 10]. With respect to the other structures, and probably to the parent nonsubstituted compound, a rotation of the cone, defined by CO(21 ), CO(22), P(3), with Co(2) as vertex, nearly around its axis occurred by about 60°; consequently Co(2) has only one equatorial ligand (PPh 3) and the other two COs are in a position intermediate between an equatorial and an axial position. Figure 3 clearly shows this arrangement. Other parameters are also involved in this rearrangement: CO(21) and CO(22) show a greater deviation from linearity (172 ° and 173°), and form angles of 81 ° and 77 ° with the adjacent C o - C o bonds (normally these values are about 100 ° for ax and eq COs). The rotation brings also P(3) into a position more tilted (35 °) with respect to the Co 3 plane than P(2) (19 ° ) and CO(32) (22°). The Co3S cluster shows a great elongation of the C o ( 1 ) - C o ( 2 ) bond (2.591(9) A), which is cis with respect to two PPh3 ligands, and shows a smaller elongation of the C o ( 2 ) - C o ( 3 ) bond which is cis to only one PPh~ ligand. This situation is in accordance with the great capability of deformation of Co3S clusters on PPh3 substitution, already observed in other
Clusters Formed from Co2(CO) Hand Me4P~S 2
Table Vl.
411
Relevant Bond Lengths (A) and Bond Angles (°) for Complex 2a
Co(I)-Co(2) Co( 1)-C(11) Co( 1 )-S(2) Co(2)-Co(3) Co(2)- C(22) Co(2)- P(3) Co(3)-C(32) Co(3)- P( I ) C(21 )-0(21 ) C(31 )-0(31 ) S(2)-P(1) P( 1)-C(2) Co(2)-Co( 1)-Co(3) Co(3)-Co( 1)-C(11 ) Co( 3)- Co( 1)- S( 1 ) Co(2)- Co( 1)-S(2) C( 1 l )-Co( 1)-S(2) Co(2) -Co( 1)- P(2) C(II )-Co( 11- P(2) S(2)-Co( 1)-- P(2) Co(1 )- Co(2)-C(21 ) Co(l )-Co(2)-C(22) C(21 )-Co(2)- C(22) Co(3)-Co(2)- S( I ) C(22)-Co(2)-S( 1 ) Co(3)-Co(2) .-P(3) C(22)- Co(2)- P(3) Co( 1)-Co(3)-Co(2) Co(2)-Co(3)-C(31 ) Co(2)-Co(3)-C(32) Co(1 )-Co(3) S(1 ) C(31 )-Co(3)-S( I ) Co( 1)-- Co(3)-. P( 1) C(31 ) - C o ( 3 ) - P ( I ) S( I )-Co(3)- P( 1) Co(2)-C(21 )- 0(21 ) Co(3)- C(31 )-0(31 } Co( 1)-S( 1 )-Co(2) Co(2)-S( 1 ) --Co(3) Co(3)-P(l ) S(2) S(2)- P( 1)-C(I ) S(2)-P( l )- C(2)
2.591(9) 1.759(14) 2.327(9) 2.534(9) 1.731(13) 2.208(8) 1.774(16) 2.194(8) 1.172(17) 1.130(17) 2.011(8) 1.803( 13 ) 59.7(2) 100.3(4) 55.5(2) 144.8(2) 97.8(5) 115.3(2) 98.6(41 91.7(2) 81.1(4) 123.3(5) 98.6(6) 54,9(2) 125.6(5) 132.8(2) 97.2(5) 62.0(2) 99.8(5) 111.2(5) 54.6(2) 147.2(5) 80.0(2) 98.2(5) 93.9(2) 171.6(10) 178.0(11 ) 73.5(2) 71.2(2) t04.6(3) 10%9(4) 108.3(5)
Co(1)-Co(3) Co(1 )-S(I) Co( 1 )-. P(2) Co(2)-C(21 ) Co(2)-S( 1 ) Co(3)-C(31 ) Co(3)-S( 1) C(I 1 )-0(11 ) C(22)-0(22) C(32) - 0(32) P(1)-C(1) Co(2)-Co( 1)-C(I 1 ) Co(2) -Co( 1 )-S(I ) C( 11 )-Co( 1 )- S( 1 ) Co(3)- Co( 1 )-S(2) S( 1 )-Co( l )- S(2) Co(3 )- Co( 1)- P(2) S(1 )-Co( 1 )- P(2) Co(1 )-Co(2)-Co(3) Co(3)-Co(2)-C(21 ) Co(3) C o ( 2 ) - C ( 2 2 ) Co(l )-Co(2)-S( 1 ) C(21 )-Co(2) - S( l ) Co( l ) -Co(2)-P(3) C(21 )-Co(2)- P(3) S( 1 )-Co(2)- P(3) Co( 1)-Co(3)-C(31 ) Co( l )-Co(3) -C(32) C(31 )-Co(3)-C(32) Co(2)-Co(3)-S(1 ) C(32)-Co(3)-S( 1) Co(2)-Co(3)- P( I ) C(32)-Co(3)- P( 1) Co( 1)-C( 11 ) - 0 ( 11 ) Co(2)-C(22)-0(22) Co(3)-C(32)- 0(32) Co( l )-S( 1)-Co(3) Co(1 )-S(2)-P(1 ) Co(3)-P(I )-C(l ) Co( 3)- P( 1) ~C(2) C(I )-P( 1)-C(2)
2.495(9) 2.165(8) 2.230(8) 1.732(15) 2.163(8) 1.806(15) 2.189(8) 1,165(16) 1.161(14) 1.133(19) 1.803(14) 99~8(4) 53.2(2) 149.3(4) 87.2(2) 99.4(2) 161.0(2) 106.2(2) 58.3(2) 123.6(5) 77.5(5) 53.3(2) 127.9(4) 138.5(2) 103.5(5) 97.3(2) 97.7(5) 157.9(5) 104.3(6) 53.9(2) 103.8(5) 139.7(2) 98.7(5) 178.5( 11 ) 173.5(12) 176,5(11 ) 69.9(2) 88.1(2) 117.5(4) 116.2(4) 102.0(6)
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Gervasio et
Fig. 3.
al.
View of the molecule of complex 2a, nearly perpendicular to the Co3 plane.
similar complexes [9, 10]. In the Co3S cluster, as in other similar complexes, the shortest side corresponds to the bridged C o - C o bond [cf. 3,5-10]. The three C o - P distances are of the same order of magnitude, while Co(1)-S(2) (2.33A av.) is significantly longer than the other three Co(n)-S(1) (2.17 A av.) distances: the same behavior is shown by Co3S clusters with one C o - C o bridged by sulfur donor ligands forming four- or five-membered rings [3, 5-10].
DISCUSSION Although the elementary compositions and formulae of the two complexes as given by Natile and co-workers [ 1] proved to be correct, none of the structures proposed by the authors was verified by the X-ray diffraction studies. As a matter of fact, those authors considered only
Clusters Formed from Co2(CO)s and Me4P2S 2
413
electron-precise closed cluster complexes since the several "butterfly" types and/or other electron-rich species with two or more excess electrons were not yet known at that time. Both complexes can be regarded as substituted derivatives of the paramagnetic complex Co3(CO)9 S [ 12 ] which is a 49-electron cluster and has the excess electron located on an antibonding cluster orbital [ 13].
Complex 1 Complex 1 can formally be derived from this parent compound by substituting two CO ligands with the Co(CO)2(PMe2) 2 fragment. Since this latter entity has five free electrons available for bonding and the removal of two CO ligands reduces the number of bonding electrons in the Co3 S trigonal pyramid only by four, complex 1 is an electron rich cluster. According the simple electron counting scheme, it contains 64 electrons which is two electrons more than required by an electron-precise butterfly arrangement of the Co4 framework. From the bonding characteristics discussed in the previous section, it is apparent that the additional two electrons occupy an orbital with a significant metal-metal antibonding character. This orbital is mainly confined to the two C o - C o bonds which link Co(2) to the Co3S trigonal pyramid. The lengths of these two bonds (2.872(1) and 2.901(1)Ä) are significantly longer than the average of the three C o - C o bonds in the Co3S unit (2.583(1) Ä). But even these latter three C o - C o bonds seem to be somewhat longer than usually found in electron-precise Co3S carbonyl clusters like [Co3(CO)7S]2S2 2.51(1)A [5], Co3(CO)7S(MeCNC6H~I) 2.503(0) Ä [6], Co3(CO)TS(CSNMe2) 2.505(1)Ä [7], Co3(CO)7 S(NHCMeS) 2.505(1)A [8], Co3(CO)9C(SCS)Co3(CO)7S 2.507(6)A [9], C03(CO)6(PPh3)(S2COMe) 2.520(1)/~ [10], C03(CO)9C(/t3-CS2) Co3(CO)7S 2.511(2) A [3], and Co3(C0)8(,u5-CS2)Co3(C0)7S 2.520( 1) Ä [3] (all are average values). Also the C o - C o bonds of the C%S trigonal pyramid are hence somewhat elongated, although not as rar as in Co3(CO)9S where this value is 2.648(4) A [12b] and which has to accomodate one electron in a metal-metal antibonding cluster orbital. A very simple reasoning based on the values of these distances leads to the conclusion that about 1/5 of the antibonding orbital filled by the two excess electrons present in 1 is located on the Co3S unit and 4/5 on the two Co-Co bonds linking Co(2) to the Co3S unit.
IR Spectrum. For compound 1, five C - O bands are observed (at 2072, 2030, 2003, 1988, and 1944 cm-L; in nujol), whereas the idealized Cs symmetry of the molecule requires all C - O modes, i.e., nine, to be active. (There are, in addition, three very weak bands and/or shoulders, at ca.
414
Gervasio et aL
2018, 1975, and 1910 cm ~, of which the lowest one is certainly a ~3C-O satellite.) Hence some of the IR-active C - O stretching normal modes are absent from the spectrum, prestimably owing to the coincidence and/or to mutual cancellation of the local vibrational dipole components. A more detailed analysis of similar cases has been given previously [3]. Some comments can be made as to the most characteristic absorption band at 2072 c m - ~ which arises from the totally symmetric in-phase mode of all nine C - O vibrators. The relatively high intensity of this band is an indication of the dipole which must be present in this molecule along the Co( 1, 3 ) . . . Co(2) axis with the c~- partial charge on the "wing'-atom Co(2) owing to the donation of electrons by the two Me2P ligands. As already mentioned above, the longer C o - C o distances in the "open" side of the cluster are an indication for the (at least partial) localization of the excess electrons near to that end of the molecule.
NMR Spe«tra. In the JH NMR spectrum (CD2C12, 300MHz, 293 K) two methyl signals appeared at 2.17 and 2.02 ppm. These, as revealed by sine-bell resolution enhancement, are rille&in doublets being the X part of an X3AA' spin system (A and A' are the two chemically equivalent phosphorous atoms). The ~3C NMR spectrum (CD2CI2/CDCI 3, 75.42 MHz, 293 K) shows only one methyl signal at 23.3 ppm which is a broadened pseudo triplet for the same reason. Under such conditions the carbonyl groups are in tast exchange on the ~3C NMR time scale as indicated by the very broad line (1'1/2=450 HZ) at about 203 ppm in the characteristic region of the terminal carbonyls. At 223 K and 100.5 MHz the pseudo triplet signal of the methyl groups broadens further which points to a decreased mobility of these groups. At the same time three sharper signals emerge from the broad carbonyl signal indicating the slow-down of the exchange at least for some of the carbonyls. The ~~P spectrum (CD2C12, 121.4 MHz, 293 K) consists of a broad singlet (vw2 = 500-600 Hz) at 153.3 ppm. We have also succeeded in recording the natural abundance ~70 NMR spectrum (40.66 MHz, 293 K, CD2C12) despite the fact that paramagnetic ions (e.g., eventual traces of Co 2+) when coordinated to oxygen can cause huge paramagnetic shift and line broadening [ 14]. The spectrum contains three lines, a broad one at 373ppm ( v w 2 = l l l Hz) and two relatively sharp resonances (v~/2 --26 Hz) at 339 and 335 ppm with integral ratios of 7:1:1, respectively. The chemical shifts are in the range reported earlier for inorganic carbonyl species [ 15]. This pattern suggests that the carbonyls attached to Co(l, 3, and 4), are in fast exchange on the ~70 NMR time scale whereas those two attached to Co(2) are already in the slow exchange
Clusters Formed from Co2(CO) ~ and Me4P2S 2
415
regime. This difference between the mobility of the CO ligands is probably due to the bridging PM% groups.
Complexes 2 and 2a As already mentioned in the experimental part, the crystals of complex 2 were not suitable for X-ray diffraction and therefore its triphenyl phosphine substituted derivative 2a was prepared. Unexpectedly, the disubstituted derivative was formed directly; no efforts were taken to prepare the monosubstituted complex. As can be concluded from the structure of 2a, complex 2 is a new member of the series of C o 3 ( C O ) 7 ( L - L ) S complexes in which L - L is a bidentate ligand using three electrons in binding to the Co3(CO)7 S cluster. The earlier examples of these complexes were already mentioned above [3,5-10]. A characteristic feature of 2a is the cis arrangement of the triphenyl phosphine ligands. Experimental observations suggest that also other stereoisomers of 2a may exist. Solid products obtained by slightly different procedures as that described in the experimental section for 2a had infrared spectra which were similar to but not identical with that of 2a. In one case we even observed that on prolonged storage the infrared spectrum of such a presumably isomeric product changed to the spectrum of 2a, suggesting isomerization. Apparently 2a is the most stable form despite the cis disubstituted structure. Two factors may account for this seemingly unexpected result. First, although it is this arrangement which places the PPh 3 ligands close to each other, at the same time this structure avoids their interference with the axial CO groups. Second, the rotation of the C o L 3 entity on C0(2) (which has been already mentioned in the section describing the structure of 2a) can also significantly decrease the interference between the two bulky ligands. Probably it is just the space requirement of the two PPh 3 groups which causes this unusual configuration. The choice of C o ( l ) instead of C0(3) as the place for the second PPh» may be the result of both steric and electronic factors: Co(3) is disfavored both because of the methyl groups on the neighboring PM% and the more basic character of phosphorus as compared to that of sulfur. All the electron precise C 0 3 ( C O ) 7 ( L - L ) S clusters may formally be regarded as if being obtained by substituting two CO ligands of the paramagneting C03(CO)9S by a three-electron ligand. However, up till now only one of them [C03(CO)7S]2S2 has been prepared starting from Co3(CO)9S [4]. All the others were obtained in "one-pot reactions" either
416
Gervasio et al.
by reacting Co2(CO)s with organic sulfur compounds [ 5 - 7 ] , or from Co 2+, CO, and the sulfur containing organic substrate [8]. Whether Co3(CO)9S is an intermediate in these reactions is uncertain. To clarify this question for the case of complex 2, the reaction between Co3(CO)9S and M e 2 P ( S ) P ( S ) M e 2 was tested. Only decomposition was observed, i.e., complex 2 is not formed via Co~(CO)gS.
IR Spectrum. Only the nonsubstituted complex 2 will be discussed here since this can be compared to the already known complexes having similar structures. The molecules of 2 are asymmetric. Hence, selection rules require seven C - O modes in the spectrum. Five of them are clearly present (2086, 2046, 2040, 2025, and 1996 cm ~; in hexane) as strong or medium intensity bands. In addition a shoulder at ca. 2015 c m ~ and a very weak band at ca. 2006 cm-~ show up in this region. A comparison of the wave-number values of the four dominating v ( C - O ) bands of compound 2 with those of the isoelectronic and isostructural Co3(CO)7(S:COMe) [ 10], viz. 2094, 2055.5, 2050, and 2033.5 c m - i clearly shows that the values of 2 are by 8-10 cm ~ lower. This difference indicates that of these two 3-electron donor ligands less negative charge is transferred to the Co3S-core by the two equivalent sulfur atoms of the xanthate than by the sulfur and the phosphorus atom of the asymmetric dimethylphosphido-sulfide ligand. NMR Spectra. Apart from the aromatic protons of the PPh 3 moieties there are three signals in the IH NMR spectrum of 2a at 300 MHz in CDCI 3 at 293K, two doublets at 2.17 ( J ( P C H ) = 9 . 9 H z ) and 2.02 (J(PCH) = 9.6 Hz) and a singlet at 1.95 ppm. This latter is assigned to the methyl group of acetonitrile present in the crystal lattice. In the 13C NMR spectrum (at 75.42 MHz in CDC13 at 293 K) the methyls attached to the phosphorus give rise to well-separated doublets (29.6 and 25.6ppm, IJ(PC) = 15.2 and 19.7 Hz, respectively). Four broadened signals appear in the terminal carbonyl region at 211.0, 207.0, 2053, and 191.3 ppm with approximate integral ratios of 2:1:1, but the stereochemically informative two-bond phosphorus-carbon couplings were not sufficiently resolved at this temperature. The 31p spectrum at 121.4 MHz in CDC13 and 293 K shows three broad lines ( v l / 2 = 3 0 0 H z ) at 56.0, 34.1, and 30.5 ppm, the high-field shift of these resonances relative to that of 1 being in agreement with the terminal character of the PPh3 ligands and the bridging position of the PMe: groups [ 16]. No signal was observed in the 170 spectrum at this time which is thought to be the consequence of a higher paramagnetic impurity level.
Clusters Formed from Coz(CO) s and Me4P2S 2
417
ACKNOWLEDGMENTS T h i s w o r k was financially s u p p o r t e d by O T K A Grant T-7444 ( H u n g a r y ) a n d by M U R S T 4 0 % (Italy). T h e a u t h o r s t h a n k Dr. R. G o b e t t o ( T o r i n o ) for d i s c u s s i o n s a n d the l o w - t e m p e r a t u r e ~3C N M R spectra o f 1.
SUPPLEMENTARY
MATERIALS AVAILABLE
T h e full lists o f b o n d lengths a n d b o n d angles, a n i s o t r o p i c coefficients, H - a t o m c o o r d i n a t e s a n d i s o t r o p i c d i s p l a c e m e n t coefficients, o b s e r v e d a n d c a l c u l a t e d s t r u c t u r e factors (42 p a g e s ) are a v a i l a b l e f r o m G G .
REFERENCES 1. 2. 3. 4.
5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16.
G. Natile, S. Pignataro, G. Innorta, and G. Bot (1972). J. Organomet. Chem. 40, 2t5. A. C. T. North, D. C. Phillips, and F. S. Mathews (1968). A«ta Cryst. A24, 351. G. Gervasio, R. Rossetti, P. L. Stanghellini, and G Bor (1982). blorg. Chem. 21, 3781. (a) G. Hogarth, J. A. Phillips, F. van Gastel, N. J. Taylor, T. B. Marder, and A. J. Carty (1988). J. Chem. Soc., C~wm. Commun. 1570; (b) G. Hogarth, N. Hadj-Bagheri, N. J. Taylor, and A. J. Carty (1990). J. Chem. Soc., Chem. Commun. 1352; (c) J. F. Corrigan, S. Doherty, N. J. Taylor, and A. J. Carty (1992). J. Am. Chem. Soc. 114, 7557; (d) J. F. Corrigan, M. Dinardo, S. Doherty, and A. J. Carty (1992). J. Cluster Sei. 3, 313; (e) J. F. Corrigan, S. Doherty, N. J. Taylor, and A. J. Carty (1993). Oqganometalli~~" 12, 993. (a) L. Markó, G. Bot, E. Klumpp, B. Markó, and G. Almäsy (1963). Chem. Ber. 96, 55; (b) D. L. Stevenson, V. R. Magnuson, and L. F. Dahl (1967). J. Am. Chem. Soc. 89, 3727. H. Patin, G. Mignani, C. Mahé, J.-Y. Le Marouille, A. Benoit, D. Grandjean, and G. Levesque (1981). J. Organomet. Chem. 208, C39. C. Mahé, H. Patin, A. Benoit, and J.-Y. Le Marouille (1981). J. Organomet. Chem. 216, C15. A. Benoit, A. Darchen, J.-Y. Le Marouille, C. Mah6, and H. Patin (1983). Organometalli«s 2, 555. C. H. Wei (1984). hwrg. Chem. 23, 2973. L. Markó, G. Gervasio, P. L. Stanghellini, and G. Bor (1985). Trans. Mer. Chem. 10, 344. G. Ger~,asio and R. Rossetti (1993). Acta Cryst. C49, 1262. (a) L. Markó, G. Bor, and E. Klumpp (1961). Chem. Ind. (London) 1491; (b) C. H. Wei and L. F. Dahl (1967). hwrg. Chem. 6, 1229. C. E. Strouse and L. F. Dahl (1969). Discuss. Faraday Soc. 47, 93. J. P. Kintzinger and H. Marsmann, in P. Diehl, E. Fluck, and R. Kosfeld (ed.), Oxygen-17 and Silicon-29 (Springer-Verlag, Berlin, 1981 ), pp. 1-64. R. Bramley, B. N. Figgis, and R. S. Nyholm (1962). Trans. Faraday Soc. 58, 1893. A. J. Carty, S. A. MacLaughlin, and D. Nucciatore, in J. G. Verkade and L. D. Quin (ed.), Phosphorous-31 NMR Spectroscopy #1 Stereochemical Analvsis (VCH Verlag, Weinheim, 1987), pp. 559-608, and references cited therein.