Synthesis and Crystal Structures of Zerovalent Platinum η²-Fumarate Bis(norbornene) Complexes and Their Application as Hydrosilylation Catalysts

Abstract

[Pt(η 2 -norbornene) 3 ] reacts with a series of electron-poor alkenes, such as dimethyl maleate, maleic anhydride, several fumarates, and fumaric acid, to give platinum complexes of the type [Pt(η 2 -alkene)(η 2 -norbornene) 2 ]. X-ray crystal structures of [Pt(η 2 -maleic anhydride)-(η 2 -norbornene) 2 ] and [Pt(η 2 -diphenyl fumarate)(η 2 -norbornene) 2 ] have been obtained. Using di-tert-butylfumaramide and diethyl dithiofumarate does not yield pure complexes. Addition of an excess of pyridine to [Pt(maleic anhydride)(norbornene) 2 ] yields the complex [Pt(η 2 -maleic anhydride)(η 2 -norbornene)(σ-N-pyridine)]. Whereas in the case of [Pt(η 2 -norbornene) 3 ] no coordination of pyridine is observed, the complex [Pt(σ-N-pyridine) 2 (η 2 -tetracyanoethylene)] is readily obtained by the addition of 1 equiv of tetracyanoethylene concomitant with or immediately after the addition of pyridine. The complexes have been employed as precatalysts in the hydrosilylation of styrene by triethylsilane. The maleate and fumarate complexes are the most stable catalysts, and the various fumarate complexes do not exhibit significant differences in their catalytic behavior.

A Coordination Controlled Aryl–Halide Oxidative Addition to Platinum

“…The X‐ray structure of complex 12 , shown in Figure 1, confirms the η 2 ‐coordination of the central carboncarbon double bond of the stilbene ( 5 ) to the metal center. The structural features are typical for Pt 0 ‐olefin complexes 12…”

“…[12] Follow-up 31 P{ 1 H} NMR experiments in THF were used to derive the rate constants, k, at 588C for the transformations: 8-12!15-19 (Figure 2 A). The reactivity differences are substantial: The stilbene complex (8), having a MeO substituent, reacts % 70 times faster than the analogous system having a NO 2 unit (12) under identical reaction conditions. The reactivity trend for these stilbene complexes is opposite that known for para-substituted aryl-bromides.…”

“…The near-zero entropy values Scheme 2. Selective formation of platinum (8)(9)(10)(11)(12)(13)(14) complexes by h 2 -coordination of compounds 1-7 followed by metal insertion into the arylÀhalide bond (15)(16)(17)(18)(19)(20)(21). (8), C1ÀC3 1.467(4), C2ÀC9 1.469(4), Br1aÀ C6 1.932(3), C12ÀN1a 1.443(7), N1aÀO1a 1.199(7), N1aÀO2a 1.270 (9), C1ÀC2 1.456(5), C1-Pt1-C2 40.21 (12), C1-Pt1-P1 106.45 (9), C1-Pt1-P2 147.71 (9), C2-Pt1-P1 145.96 (9), C2-Pt1-P2 108.28 (9), P1-Pt1-P2 105.59(3).…”

Palladium–(N‐Heterocyclic Carbene) Hydrogenation Catalysts

“…It is known that fumarates are stronger alkene ligands in platinum(0) complexes than maleic anhydride and quinones. [10] Indeed, complexes 4 and 5 do enter the catalytic cycle owing to the weaker alkene ligands. However, during hydrogenation, considerable amounts of (E)-1-phenylpropene and alkane are observed for these catalysts.…”

Palladium–(N‐Heterocyclic Carbene) Hydrogenation Catalysts

“…Complex 3 does not catalyze the hydrogenation at all: it would appear that the dimethyl fumarate complexes coordinate too strongly to create vacant sites needed for catalysis. It is known that fumarates are stronger alkene ligands in platinum( 0 ) complexes than maleic anhydride and quinones 10. Indeed, complexes 4 and 5 do enter the catalytic cycle owing to the weaker alkene ligands.…”