Comparison of the Reactivity of Platinum(II) and Platinum(0) Complexes with Iminophosphine and Phosphinocarbonyl Ligands

Iminophosphines 2-(PPh 2 )C 6 H 4 C(R)═NR′ (L) (R = H, Me; R′ = 2,6-Me 2 C 6 H 3 or 2,6-Pr i 2 C 6 H 3 ) react with Pt(II) precursors to form chelated P,N complexes [PtLX 2 ] (X = Me, Et, Cl), whereas with [Pt(C 7 H 10 ) 3 ] (C 7 H 10 = norbornene) and other labile Pt(0) precursors coordination is via phosphorus and chelation is not observed. However, activation of the imine H or the methyl C–H bond of the ketoimine affords P,C metallacyclic hydride complexes [ PtH(PPh 2 C 6 H 4 C═NR′)L] and [ PtH(PPh 2 C 6 H 4 C(═NR′) CH 2 )L], respectively. Under more forcing conditions the ketoimine complex undergoes a second metalation reaction, forming cis- and trans -bis- P,C -metallacyclic complexes. By contrast, reaction of the phosphinocarbonyl ligands 2-(PPh 2 )C 6 H 4 C(R)═O (L′) (R = H, Me) with Pt(II) precursors always affords bis-monodentate complexes [PtL′ 2 X 2 ] initially. Where X = Me, methane elimination occurs, forming five- (R = H) or six- (R = Me) membered P,C metallacyclic complexes, [ PtMe(PPh 2 C 6 H 4 CO)L′]. On heating, the second phosphinocarbonyl metalates, forming cis - and trans -bis- P,C -metallacyclic complexes. X-ray crystallography of the cis -metalla-β-diketone complex [ Pt(PPh 2 C 6 H 4 CO) 2 ] established the closeness of the carbonyl oxygen atoms, which readily capture H + and other cations, forming stable complexes. These bis-chelate complexes also form readily from the reaction of the phosphinocarbonyls with [Pt(C 7 H 10 ) 3 ] via an intermediate norbornyl complex (R = H) or a 5,6-ring bis-chelate (R = Me) in which a hydride is transferred from one ketone to partially reduce the second ketone.