Synthesis and Reactions of Heterodinuclear Organoplatinum Complexes Having an Unsymmetrical PN Ligand

Abstract

A series of heterodinuclear organoplatinum complexes having an unsymmetrical PN ligand (Et2NC2H4PPh2-κ2N,P)RPt−MLn [MLn = MoCp(CO)3, R = Me (1), R = Ph (2); MLn = WCp(CO)3, R = Me (3), R = Ph (4); MLn = Co(CO)4, R = Me (5), R = Ph (6)] have been synthesized by metathetical reactions of PtR(NO3)(Et2NC2H4PPh2-κ2N,P), which is prepared in situ from PtRCl(Et2NC2H4PPh2-κ2N,P) (R = Me, Ph) and AgNO3, with Na[MLn]. Analogous complexes with a bidentate nitrogen ligand (tmeda-κ2N,N‘)RPt−MoCp(CO)3 [R = Me (7), Ph (8)] are also prepared by ligand exchange reaction of (cod)RPt−MoCp(CO)3 with TMEDA (N,N,N‘,N‘-tetramethylethylenediamine). These complexes are characterized by NMR and IR spectroscopies and elemental analyses, and the molecular structure of 2 is determined by X-ray structure analysis. Variable-temperature NMR study reveals the reversible partial dissociation of the Pt−N bond in 2 and 4, where the kinetic parameters are estimated by line shape analysis of 2: ΔG273⧧ = 57.9 kJ mol-1, ΔH⧧= 49.8 kJ mol-1, ΔS⧧ = −29.7 J mol-1 K-1. Treatment of 1−4 with CO causes partial dissociation of the amino ligand moiety in the PN ligand from the Pt center to form (Et2NC2H4PPh2-κ1P)(CO)RPt−MCp(CO)3 [M = Mo, R = Me (9), Ph (10); M = W, R = Me (11), Ph (12)]. Heating of 9 at 70 °C induces CO insertion to give an equilibrium mixture of (Et2NC2H4PPh2-κ2N,P)(MeCO)Pt−MoCp(CO)3 (14) with 9 in 3:2 ratio. In contrast, the Pt−Co complex 5 with a PN ligand smoothly yields the acetyl complex (Et2NC2H4PPh2-κ2N,P)(MeCO)Pt−Co(CO)4 (15) on interaction with CO at room temperature. On the other hand, in the reactions of 1 with Et2NC2H4PPh2 or phosphorus ligand such as PMe3, PEt3, PPh3, and P(OMe)3, heterolytic cleavage of the Pt−Mo bond takes place to give ionic complexes [PtMe(PR3)(Et2NC2H4PPh2-κ2N,P)]+[MoCp(CO)3]- [PR3 = Et2NC2H4PPh2 (17), PMe3 (18), PEt3 (19), PPh3 (20), P(OMe)3 (21)].