Synthesis of Pt(II)−Pt(II) and Pt/Pd(II)−Pt(0) Monoalkynylphosphine Bridging Complexes

The monoalkynylphosphine complexes cis- [Pt(C 6 F 5 ) 2 (PPh 2 C⋮CR)(tht)] (R = Ph 1a, Tol 1b, t Bu 1c, tht = tetrahydrothiophene) have been prepared by bridge splitting [{Pt(C 6 F 5 ) 2 (μ-tht)} 2 ] or by displacement of only one tht ligand from cis- [Pt(C 6 F 5 ) 2 (tht) 2 ] with PPh 2 C⋮CR. Complexes 1 react with cis- [Pt(C 6 F 5 ) 2 (thf) 2 ] to give binuclear derivatives [(C 6 F 5 ) 2 Pt(μ-tht)(μ-1κ P:2η 2 -PPh 2 C⋮CR)Pt(C 6 F 5 ) 2 ] (R = Ph 2a, Tol 2b, t Bu 2c ), containing a mixed tht/PPh 2 C⋮CR bridging system. In contrast, treatment of 1 with [Pt(η 2 -C 2 H 4 )(PPh 3 ) 2 ] affords mixed-valence Pt(II)−Pt(0) complexes [{(C 6 F 5 ) 2 (tht)Pt(μ-1κ P:2η 2 -PPh 2 C⋮CR)}Pt(PPh 3 ) 2 ] (R = Ph 3a, Tol 3b ) stabilized by only one κ P:η 2 bridging alkynyl phosphine. The molecular structures of 2a and 3a have been confirmed by single-crystal X-ray diffraction. Similarly, reactions of cis -bis(diphenylphosphino)alkyne complexes cis- [M(C 6 F 5 ) 2 (PPh 2 C⋮CR) 2 ] and cis -[Pt(C⋮CR‘) 2 (PPh 2 C⋮CR) 2 ] (M = Pt, Pd; R = Ph, Tol; R‘= Ph, t Bu) with 1 or 2 equiv of [Pt(η 2 -C 2 H 4 )(PPh 3 ) 2 ] yield the corresponding mixed-valence binuclear complexes cis- [{(C 6 F 5 ) 2 M(PPh 2 C⋮CR)(μ-1κ P:2η 2 -PPh 2 C⋮CR)}Pt(PPh 3 ) 2 ] (M = Pt, R = Ph 4a, Tol 4b; M = Pd, R = Ph 5a, Tol 5b ) and cis- [{(C⋮CR‘) 2 Pt(PPh 2 C⋮CR)(μ-1κ P:2η 2 -PPh 2 C⋮CR)}Pt(PPh 3 ) 2 ] (R‘ = Ph, R = Ph 6a, Tol 6b; R‘ = t Bu, R = Ph 7a, Tol 7b ), bearing only one PPh 2 C⋮CR η 2 -coordinated to a Pt(0)(PPh 3 ) 2 fragment.