Alkylidyne ligand bridging

Reactions of alkynes with trinuclear group 6-group 9 clusters incorporating bridging alkylidyne ligands proceeded by coupling the C-donor ligands. 

The structure of 11a has been established by X-ray diffraction. The compounds 11 are 30-cluster valence-electron (CVE) dimetal species, and are therefore electronically unsaturated. The electron distribution within the W(fi-C)fth rings may be represented by various canonical forms. However, that shown, which implies that the W=C bond in the ( 5-C2B9H9R 2)(OC)2-W=CC6H4Me-4 moiety formally contributes three electrons to the rhodium center (16-electron valence shell), accords with other results from our laboratory involving electronically unsaturated dimetal compounds with bridging alkylidyne ligands 18). 

As will be seen in later sections, the complexes in which the heteronuclear metal-metal bonds are bridged by agostic B—H—- metal interactions are intermediates in a variety of reactions involving the carbaborane cages and the /i-alkylidyne ligands. 

COMPOUNDS WITH BRIDGING ALKYLIDENE AND ALKYLIDYNE LIGANDS. 

The results described in this paper suggest that further studies in this area would be very profitable. The heteronuclear metal —metal bonded species will have a rich chemistry at the metal centres, particularly in those cases where bridging alkylidene or alkylidyne ligands are present. 

Efforts by Krouse and Schrock to prepare polyenynes by a metathetical process led to the preparation of several dinuclear complexes bridged by unsaturated bisalkylidyne ligands [Eq. (194)] (199). Two possible reasons for the failure to obtain the desired polymers were mentioned. The dinuclear metal-capped species were found to be thermodynamically more stable than mononuclear complexes with terminal alkylidyne ligands, and the solubility of the oligomers, if formed, appears to decrease rapidly with increasing molecular weight. 

Addition of 2 eq HC1 to (22) in ether produced a thermally unstable bis(alkylidene) complex, which upon addition of excess PMe3 generated binuclear (41). The bridging alkylidyne ligands of (41) exhibited inequivalent Ta—C bond lengths of 2.073(6)-2.099(6) A and 1.922(6)-1.942(7) A, consistent with the different nature of the Ta centers.73,74... 

The addition of sulfur to the bridging alkylidyne ligand in TpMoFe(ju-CC6H4Me-4) (CO)5 provides the heterobimetallic thioacyl complex TpMoFe(/i-f/-SCR)(CO)5, in... 

Scheme 82. Formation of tetranuclear WRU3 cluster containing a triply bridging alkylidyne ligand...

Like other dinuclear complexes containing bridging alkylidyne ligands [5], the chemistry of the Angelici s thiocarbyne [Fe2(ti-CSR)(p-CO)(CO)2Cp2] (l) is dominated by the electrophilic character of the i -carbyne carbon atom. In fact 1 reacts with a variety of nucleophiles such as RS" (R = Me, PhBz), PhSe , BH4" [6] and CN [7] to give the corresponding carbene derivatives 2, 3 and 4 (Scheme 1). 

One hexanuclear structure [W6(M-H)4(M-OPr )7(ju,-CPr )(OPr )5(H)] has been reported. This is based on the familiar octahedral We cluster configuration with 12 bridging (4 hydride, 7 isopropoxide, 1 alkylidyne) ligands and 6 terminal (5... 

Byers, P.K, Carr, N. and Stone, F.G.A. (1990) Chemistry of polynuclear metal complexes with bridging carbene or carbyne ligands. Part 106. Synthesis and reactions of the alkylidyne complexes [M ( CR)(CO)2 (C6F5)AuC(pz)3 j (M = W or Mo, R — alkyl or aryl, pz — pyrazol-l-yl) crystal structure of pjC PtAu(C6F5)( l3-CMe)(CO)2(PMe2Ph)2 (C6F5)AuC(pz)3 ]. Journal of the Chemical Society, Dalton Transactions, (12), 3701—3708. 

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