High-pressure methods as a tool in organometallic syntheses: facilitation of oxidative addition to platinum(II)

Abstract

High-pressure (2 GPa) batch reactors now commercially available may offer substantial accelerations of organometallic syntheses, without resort to heating, when the activation process is multicentered or involves the generation and solvation of ions. As an example of the latter class of reactions, the kinetics of the oxidative additions of methyl and ethyl iodides (RI) to dimethyl(2,2'-bipyridine)platinum(II) in acetone have been studied over the pressure range 0-200 MPa. The volumes of activation Av,*, if assumed to be constant over this range, are -11.7 2 0.3 and -9.7 2 0.7 cm3 mol-', respectively, implying an acceleration of ca. 3000-fold for a batch synthesis of this sort at 2 GPa. However, a possible slight pressure dependence of Av,* may reduce this acceleration to ca. 1 000-fold. The Av,* data and the 500-fold retardation on going from R = Me to R = Et are consistent with an SN2 attack of ~t " on the a-carbon in the alkyl iodides, forming I-and [RMe2Pt(bpy)]+.Key words: volumes of activation, high pressure, oxidative addition, platinum(II), organometallic syntheses. The routine use of pressures on the order of 1 GPa (1 0 kbar) as a synthetic tool has gained acceptance among organic chemists (1-9), but to date has not found significant application in organometallic chemistry. Apart from the obvious advantage of producing enhanced activities of gaseous reactants, pressure P can influence the maximum attainable yield of a reaction through the equilibrium constant K if the reaction volume A V (the molar volume of the products minus that of the reactants) is nonzero:Received January 24, 1996. This paper is dedicated to Professor Howard C. Clark ill recognition of his contributions to Cai~ndian chemistry.

Activation and Reaction Volumes in Solution. 3

“…The same is true for the NMR coalescence of the two methyl groups in N,N-dimethyltrichloroacetamide; 483 the activation volume for this process is positive as was observed by Lu ¨demann for a host of amides. 1 A negative activation volume was found by Yamada and Sera 484 for the phenyl group rotation inside the cavity of a [12]paracyclophane, and they interpreted this classically as the result of more efficient space utilization in the transition state (entries [245][246].…”

Water as a key ingredient in the synthesis of platinum H‐phosphonate complexes and catalytic cascade reactions involving the hydration of alkynes and hydrogen/deuterium exchange reaction

“…H‐spirophosphorane ligand 2,2,3,3,8,8‐hexamethyl‐1,4,6‐trioxa‐9‐aza‐5λ5‐phosphaspiro[4.4]nonane HP (OCMe 2 CMe 2 O)(OCH 2 CMe 2 NH) 46 and platinum complexes [Pt (COD)Cl 2 ] 47 and [PtCl 2 (PPh 3 ) 2 ] 48 were prepared according to the literature methods. The H‐phosphonate H(O)P(OCMe 2 CMe 2 O) known as 4,4,5,5‐tetramethyl‐1,3,2‐λ 5 ‐dioxaphospholan‐2‐one ligand was prepared according to two procedures: the one already known in the literature utilizing pinacol and phosphorus trichloride followed by hydrolysis 49 and the second one reported below.…”