Bridging and Terminal (Phosphanido)platinum Complexes

The PR 2 – group (the phosphanido group, according to the modern IUPAC rules) possesses a strong nucleophilicity, a high bridging tendency and a remarkable flexibility. This review addresses the issue of (phosphanido)platinum complexes, subdividing them into terminal and bridging species. Terminal (phosphanido)platinum complexes are usually prepared by deprotonation of a coordinated secondary (or primary) phosphane on a cationic Pt II complex, by an appropriate base. The terminally bonded phosphanide group shows no tendency to form multiple bonds with platinum: in all crystallographically characterised Pt complexes, the terminal phosphanido P atom is pyramidal. Due to the high nucleophilicity granted by the presence of the active lone pair on P, terminal (phosphanido)platinum complexes react with molecules such as O 2 and S 8 , and they can be used for the synthesis of dimetallic compounds upon reaction with suitable metal fragments. The known Pt I phosphanido‐bridged complexes are dinuclear, diamagnetic and endowed with a strong Pt–Pt bond. The μ‐PPh 2 bridge in Pt I dimers arises often by (thermal) activation of the P–C bond in coordinated PPh 3 or dppm. Pt I phosphanido‐bridged complexes are also prepared by reaction of (dichlorido)platinum complexes with reagents such as Na, NaOH, alcohols. For such complexes a multifaceted reactivity, including the substitution of a terminal ligand, the reaction with electrophiles such as H + and its isolobal analogues, the insertion into the μ‐P–Pt bond, has been reported. Hydridophosphanido complexes are formed by oxidative addition of a P–H bond onto zero‐valent Pt complexes, by protonation of Pt I dimers or by action of BH 4 – on halido species. Dehydrochlorination of secondary (and primary) phosphane complexes gives chlorido complexes which are mostly prepared in the anti ‐[(PRR′ 2 )(Cl)Pt(μ‐PR″ 2 )] 2 geometry. Chiral complexes are obtained when asymmetric phosphanido P atoms are present in the molecule. A rich coordination chemistry has been developed on organometallic phosphanido Pt complexes bearing the pentafluorophenyl group. In this framework, a great number of Pt complexes of various nuclearity have been crystallographically characterised and their reactivity towards oxidants studied. The class of polynuclear phosphanido Pt complexes is represented by triangulo species, in which the bridging phosphanide group is typically μ‐PPh 2 or μ‐P t Bu 2 , by linear complexes of various nuclearity and by bent species stemming from the presence of a triply bridging diphenylphosphanido ligand in the molecule. Applications of phosphanido Pt complexes in catalysis and materials chemistry are also discussed. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)