Reaction of [Tp*(CO) 2 MtC-PdC(NMe 2 ) 2 ] [1a, M ) Mo; 1b, W; Tp* ) HB(3,5-Me 2 pz) 3 ] with 2 molar equiv of [Au(CO)Cl] afforded the trinuclear complexes [Tp*(CO) 2 MtC-P(AuCl) 2 C(NMe 2 ) 2 ] 2a (M ) Mo) and 2b (M ) W). In marked contrast to this the arsenic analogues [Tp*(CO) 2 MtC-AsdC(NMe 2 ) 2 ] (3a, M ) Mo; 3b, M ) W), when treated with the gold complex, give rise to AsdC cleavage with formation of the gold carbene complex [ClAuC-(NMe 2 ) 2 ] (5) and the functionalized cyclotriarsanes [{Tp*(CO) 2 MtC-As} 3 ] 4a (M ) Mo) and 4b (M ) W). Compounds 2a,b and 4a,b have been characterized by IR and 1 H and 13 C NMR spectroscopy. In addition, the molecular structures of 2a, 2b, and 5 have been determined by single-crystal X-ray structural analyses.

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Et), which have been characterized by IR, IH-, I3C-and 31P-NMR spectroscopy. In addition, the molecular structure of 5b has been elucidated by a single-crystal X-ray structure determination.

Reaction of the carbyne complexes Tp‘(CO)2M⋮C−PC(NR2)2 (1, 2) [Tp‘ = HB(3,5-Me2C3HN2)3; M = Mo (1, 3); W (2, 4); R = Me (a); Et (b)] with methyl trifluoromethanesulfonate afforded the orange-red salts [Tp‘(CO)2M⋮C−P(Me)C(NR2)2]SO3CF3 (3, 4), the cations of which can be considered as methylphosphines featuring additional bisaminocarbenium- and metallaalkynyl substituents. Analogously, complex Tp‘(CO)2W⋮C−PC(NEt2)2 (2b) was protonated with ethereal HBF4 in ether at the phosphorus atom to give [Tp‘W⋮C−P(H)−C(NEt2)2]BF4 (5), which in CH2Cl2 solution experienced a clean rearrangement to the metallaphosphirene (6). Treatment of 2b with F3CSO3H led directly to (6‘). The molecular structures of 4b and 6‘ were established by X-ray structure analysis.