Synthesis, characterisation and reactivity of group six alkylidynes bearing the tridentate phosphine PPh(C2H4PPh2)(2) 'triphos'. Crystal structure of mer-[W(NCMe)( CC6H4Me-4){PPh(C2H4PPh2)(2)}(CO)][BF4]

Reaction between [WBr(≡CC6H4Me-4)(NC5H5Me-4)2(CO)2] and the tridentate, linear, phosphine PPh(CH2CH2PPh2)2 (triphos) in refluxing toluene affords mer-[WBr(≡CC6H4Me-4){PPh(C2H4PPh2)2}(CO)], 1. Halide abstraction (with TIBF4) in CH2Cl2 solvent results in carbonyl scavenging to afford the cationic dicarbonyl species fac-[WBr(≡CC6H4Me-4){PPh(C2H4PPh2)2}(CO)2][BF4], 2, whereas removal of the halide in acetonitrile solvent affords the complex mer-[W(NCMe)(≡CC6H4Me-4){PPh(C2H4PPh2)2}(CO)][BF4], 3. Protonation of 1 (with HBF4 · OEt2) results in the formation of the alkylidene complex mer-[WBr{=C(H)C6H4Me-4}{PPh(C2H4PPh2)2}(CO)][BF4], 4. Methylation of 1 affords the methyl/alkylidyne complex mer-[WCH3(≡CC6H4Me-4){PPh(C2H4PPh2)2}(CO)], 5, which can be protonated to form [WCH3{=C(H)C6H4Me-4}{PPh(C2H4PPh2)2}(CO)][BF4], 6. The new complexes have been fully characterised by multinuclear NMR spectroscopy and, additionally, for 3 by a single crystal X-ray diffraction study. © 1997 Elsevier Science S.A