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

Iminophosphines 2-(PPh2)C6H4C(R)NR′ (L) (R = H, Me; R′ = 2,6-Me2C6H3 or 2,6-Pri2C6H3) react with Pt(II) precursors to form chelated P,N complexes [PtLX2] (X = Me, Et, Cl), whereas with [Pt(C7H10)3] (C7H10 = 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(PPh2C6H4CNR′)L] and [PtH(PPh2C6H4C(NR′)CH2)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-(PPh2)C6H4C(R)O (L′) (R = H, Me) with Pt(II) precursors always affords bis-monodentate complexes [PtL′2X2] initially. Where X = Me, methane elimination occurs, forming five- (R = H) or six- (R = Me) membered P,C metallacyclic complexes, [PtMe(PPh2C6H4CO)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(PPh2C6H4CO)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(C7H10)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.