Synthesis and characterization of mono- and binuclear platinum complexes containing terminal and bridging diynyldiphenylphosphine ligands

Abstract

A series of mononuclear platinum complexes containing diynyldiphenylphosphine ligands [cis-Pt(C₆F₅)₂(PPh₂CCC₆H₄CCR)L]ⁿ (n = 0, L = tht, R = Ph 2a, Bu^t2b; L = PPh₂CCC₆H₄CCR, 4a, 4b; n = −1, L = CN⁻, 3a, 3b) has been synthesized and the X-ray crystal structures of 4a and 4b have been determined. In order to compare the η²-bonding capability of the inner and outer alkyne units, the reactivity of 2–4 towards [cis-Pt(C₆F₅)₂(thf)₂] or [Pt(η²-C₂H₄)(PPh₃)₂] has been examined. Complexes 2 coordinate the fragment “cis-Pt(C₆F₅)₂” using the inner alkynyl fragment and the sulfur of the tht ligand giving rise the binuclear derivatives [(C₆F₅)₂Pt(µ-tht)(µ-1κP:2η²-C^α,C^β-PPh₂CCC₆H₄CCR)Pt(C₆F₅)₂] (R = Ph 5a, Bu^t5b). The phenyldiynylphosphine complexes 2a, 3a and 4a react with [Pt(η²-C₂H₄)(PPh₃)₂] to give the mixed-valence Pt(II)–Pt(0) complexes [{(C₆F₅)₂LPt(µ-1κP:2η²-C⁵,C⁶-PPh₂CCC₆H₄CCPh)}Pt(PPh₃)₂]ⁿ (L = tht 6a, CN 8a and PPh₂CCC₆H₄CCPh 9a) in which the Pt(0) fragment is η²-complexed by the outer fragment. Complex 6a isomerizes in solution to a final complex [{(C₆F₅)₂(tht)Pt(µ-1κP:2η²-C^α,C^β-PPh₂CCC₆H₄CCPh)}Pt(PPh₃)₂] 7a having the Pt(0) fragment coordinated to the inner alkyne function. In contrast, the tert-butyldiynylphosphine complexes 2b and 3b coordinate the Pt(0) unit through the phosphorus substituted inner acetylenic entity yielding 7b and 8b. By using 4a and 2 equiv. of [Pt(η²-C₂H₄)(PPh₃)₂] as precursors, the synthesis of the trinuclear complex [cis-{(C₆F₅)₂Pt(µ-1κP:2η²-C⁵,C⁶-PPh₂CCC₆H₄CCPh)₂}(Pt(PPh₃)₂)₂] 10a, bearing two Pt(0)(PPh₃)₂ η²-coordinated to the outer alkyne functions is achieved. The structure of 7a has been confirmed by single-crystal X-ray diffraction.