SYNTHESIS OF THE SALTS [N(PPH3)2]2[M(CO)3(ETA-6-7,9-ME2-7,9-C2B10H10)] (M=MO OR W) AND THEIR USE AS REAGENTS FOR PREPARING POLYNUCLEAR METALLACARBORANE CLUSTER COMPOUNDS

Treatment of the compounds [M(CO)3(NCEt)3] (M = Mo or W) with Na2[nido -7,9-Me2-7,9-C2B10H10] in thf (tetrahydrofuran) affords the complex an ions [M(CO)3(eta6-7,9-Me2-7,9-C2B10H10)]2-which have been isolated as their [N(PPh3)2]+ salts [2a, M = Mo; 2b, M = W]. Reactions of these re agents With CiS-[PtCl2(CO)(PPh3)] in thf, in the presence of TIPF6, yi eld separable mixtures of the di- and trinuclear metal species [MPt(CO )4(PPh3)(eta6-7,9-Me2-7,9-C2B10H10)] [4c, M = Mo; 4d, M = W] and Pt2(m u-CO)(CO)3(PPh3)2(eta6-7,9-Me2-7,9-C2B10H10)] [8a, M = Mo; 8b, M = W], respectively. The structure of compound 8a has been established by X- ray diffraction. Crystals are monoclinic, space group P2(1)/n (No. 14) with a = 13.047(2) angstrom, b = 13.856(2) angstrom, c = 27.103(6) an gstrom, beta = 102.13(2)-degrees, and Z = 4. The core of the molecule consists of a triangle of metal atoms [Mo-Pt 2.707(l) and 2.950(1) ang strom, Pt-Pt 2.747(1) angstrom] with the molybdenum atom ligated by a 7,9-Me2-7,9-C2B10H10 carborane cage, bound in the normal hexahapto man ner, and one terminal carbonyl group. One of the Mo-Pt vectors is semi bridged by two CO groups. Each platinum atom carries a PPh3 ligand and the Pt-Pt vector is bridged essentially symmetrically by a carbonyl g roup [Pt-CO 1.996(8) and 2.026(7) angstrom]. In addition, the BH bond which is in a site beta to the carbon atoms of the CBCBBB hexagonal ri ng of the carborane ligand is involved in an exopolyhedral three-cente r, two-electron B-H half arrow pointing right Pt interaction. Treatmen t of the salts 2 with [PtCl2(cod)] (cod = cycloocta-1,5-diene) in the presence of TIPF6 gives the trimetal compounds sigma,sigma':eta6-7,9-M e2-7,9-C2B10H8)(CO)2(cod)2] [7a, M = Mo; 7b, M = W] containing two exo polyhedral B-Pt sigma-bonds. The cod ligands present in 7a may be disp laced by [W(=CC6H4Me-4)(CO)2(eta5-C5H5)] to afford the pentanuclear co mplex [MoW2Pt2(mu-CC6H4Me-4) (mu3-CC6H4Me-4) eta6-7,9-Me2-7,9-C2B10H8- 12-OC)(CO)7-(eta5-C5H5)2] (9). A single-crystal X-ray diffraction anal ysis of 9 has been carried out. Crystals are orthorhombic, space group Pbcn (No. 60) with a = 29.736(4) angstrom, b = 18.077(1) angstrom, c = 18.100(2) angstrom, and Z = 8. The molecular structure of 9 consists of an almost planar chain of MoPtWPtW atoms with both an edge-bridgin g [mu-C-W 1.79(4) angstrom, mu-C-Pt 1.93(4) angstrom] and a triply-bri dging [mu-C-W 1.99(4) angstrom, mu-C-Pt 2.05(4) and 2.20(4) angstrom] tolylmethylidyne ligand. A novel feature of the structure is the prese nce of a CO group bridging one of the W-Pt bonds and also attached thr ough its oxygen atom to the boron atom that is in a site alpha to the carbon atoms of the CBCBBB ring of the carborane ligand that is eta6-c oordinated to the Mo atom. In addition, the beta boron atom of this ri ng, CBCBBB, forms an exopolyhedral B-Pt sigma-bond to the same platinu m atom that is involved in the BO-Pt-W interaction. Upon treatment wit h PMe3, the terminal [W(=CC6H4Me-4)(CO)2(eta5-C5H5)] molecule present in 9 is displaced to yield the tetranuclear metal complex sigma:eta6-7 ,9-Me2-7,9-C2B10H8-12-OC)(CO)5(PMe3)2( eta5-C5H5)] (10). The new metal lacarborane cluster compounds have been characterized by IR and NMR sp ectroscopy, in addition to the X-ray diffraction studies.