Bridging and Terminal (Phosphanido)platinum Complexes

Abstract

The PR2– 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 PtII 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 O2 and S8, and they can be used for the synthesis of dimetallic compounds upon reaction with suitable metal fragments. The known PtI phosphanido‐bridged complexes are dinuclear, diamagnetic and endowed with a strong Pt–Pt bond. The μ‐PPh2 bridge in PtI dimers arises often by (thermal) activation of the P–C bond in coordinated PPh3 or dppm. PtI 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 PtI dimers or by action of BH4– 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‐PPh2 or μ‐PtBu2, 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)

Synthesis and Reactivity of the Unsaturated Trinuclear Phosphanido Complex [(C6F5)2Pt(μ-PPh2)2Pt(μ-PPh2)2Pt(PPh3)]

“…The Pt(1)···Pt(2) distance is 3.6760(4) Å, excluding any intermetallic interaction. Accordingly, the Pt(1)−P(1)−Pt (2) and Pt(1)−P(2)−Pt(2) angles are broad (ca. 105°; Table 1).…”

“…Complex 1 is a trinuclear species, with the three Pt atoms forming an almost linear array [the value of the Pt(1)−Pt(2)−Pt(3) angle is 178.14(1)°]. The coordination environment of Pt(1) is squareplanar, with two pentafluorophenyl ligands mutually cis and two phosphanido ligands bridging Pt (1) and Pt (2). The Pt(1)···Pt(2) distance is 3.6760(4) Å, excluding any intermetallic interaction.…”

Donor Behaviour of Anionic and Asymmetric Phosphanido Derivatives of Platinum and Palladium

“…In all cases, the 31 P{ 1 H} NMR spectra of 1-7 at 298 K showed two mutually coupled doublets in the region δ = -125 to -60 ppm owing to the bridging phosphanides P 1 and P 2 (see Table 7), along with a complex signal at lower fields (δ = 4-16 ppm) ascribable to the Agbonded PPh 3 ligand. [56] The 2 J P,P coupling constants are higher for the Pt-Pd systems than for the Pt-Pt ones, and the signal attributed to the Ag-bonded P 3 Ph 3 ligand consists of the superimposition of the doublets owing to coupling of P 3 with 107 Ag and 109 Ag nuclei. [56] The 2 J P,P coupling constants are higher for the Pt-Pd systems than for the Pt-Pt ones, and the signal attributed to the Ag-bonded P 3 Ph 3 ligand consists of the superimposition of the doublets owing to coupling of P 3 with 107 Ag and 109 Ag nuclei.…”

Synthesis of Heterodimetallic Complexes by Reaction of a Terminal Phosphido Pt Complex with Metal‐Based Nucleophiles and Electrophiles

“…The 31 P{ 1 H} NMR spectrum of 2 at 298 K showed three doublets of doublets at δ = 246.2 23.6 and 20.9 ppm, each flanked by 195 Pt satellites arising from direct 31 P-195 Pt couplings ( Table 2). The signal at δ = 246.2 ppm is ascribable to the bridging phosphanide ligand (P 1 ) that subtends a Pt-Co bond, [4] and those at δ = 23.6 and 20.9 ppm are attributed to the coordinated PHCy 2 ligand (P 2 and P 3 , respectively). The 13 C{ 1 H} attached proton test (APT) spectrum at 298 K showed only a broad signal at δ = 212.9 in the carbonyl region owing to the averaged resonances of the CO ligands; this suggests that the three carbonyl ligands are in fast mutual exchange at room temperature.…”

“…[1] Two important synthetic strategies commonly used for the preparation of heterodimetallic complexes are: (1) the nucleophilic substitution of a chloride ligand by an electron-rich (usually anionic) metal complex [2] and (2) the reaction between a "metalloligand" and a suitable metal complex often endowed with a labile ligand such as tetrahydrofuran (thf) or a diene. M(μ-PR 2 )MЈ systems, which are of great importance owing to their stability and multifaceted reactivity, [4] have been obtained by reactions of terminal phosphanido complexes either with chlorido complexes (terminal [5] or bridging) [6] or with MЈL n complexes bearing a poorly coordinating ligand. M(μ-PR 2 )MЈ systems, which are of great importance owing to their stability and multifaceted reactivity, [4] have been obtained by reactions of terminal phosphanido complexes either with chlorido complexes (terminal [5] or bridging) [6] or with MЈL n complexes bearing a poorly coordinating ligand.…”