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

A series of mononuclear platinum complexes containing diynyldiphenylphosphine ligands [cis-Pt(C6F5)2(PPh2CCC6H4CCR)L]n (n = 0, L = tht, R = Ph 2a, But2b; 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-Cα,Cβ-PPh2CCC6H4CCR)Pt(C6F5)2] (R = Ph 5a, But5b). 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-Cα,Cβ-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.