The critical role played by water in controlling Pd catalyst speciation in arylcyanation reactions

TY - JOUR

T1 - The critical role played by water in controlling Pd catalyst speciation in arylcyanation reactions

AU - Bray, Joshua T.W.

AU - Ford, Mark J.

AU - Karadakov, Peter B.

AU - Whitwood, Adrian C.

AU - Fairlamb, Ian J.S.

N1 - This is an author-produced version of the published paper. Uploaded with permission of the publisher/copyright holder. Further copying may not be permitted; contact the publisher for details

PY - 2019/1/1

Y1 - 2019/1/1

N2 - Pd-Catalyzed arylcyanation reactions are widely applied in academic and industrial problems. We demonstrate for the first time that water acts as a powerful trigger for heterogeneous catalysis in arylcyanation reactions. A selection of trans-Pd(OAc)2(HNR2)2 precatalysts have been synthesized, characterized and kinetically scrutinized as precatalysts for the Pd-catalyzed arylcyanation of aryl bromides. Kinetic and mechanistic studies using in operando infrared spectroscopic analysis reveal the key role played by water, specifically deriving from K4[Fe(CN)6]·3H2O, in facilitating a remarkable switch in mechanism from a homogeneous to heterogeneous catalytic manifold. Evidence for heterogeneity includes sigmoidal kinetic traces, an order in Pd of 0.26 and catalyst turnover sequestration upon addition of excess Hg. The TOF and TON values recorded using K4[Fe(CN)6] (<220 ppm H2O) were higher than when using K4[Fe(CN)6]·3H2O (>4000 ppm H2O). Catalytic cycles are configured according to the experimental evidence gained from this study. We conclude that water plays a critical role in Pd catalyst speciation in arylcyanation chemistry.

AB - Pd-Catalyzed arylcyanation reactions are widely applied in academic and industrial problems. We demonstrate for the first time that water acts as a powerful trigger for heterogeneous catalysis in arylcyanation reactions. A selection of trans-Pd(OAc)2(HNR2)2 precatalysts have been synthesized, characterized and kinetically scrutinized as precatalysts for the Pd-catalyzed arylcyanation of aryl bromides. Kinetic and mechanistic studies using in operando infrared spectroscopic analysis reveal the key role played by water, specifically deriving from K4[Fe(CN)6]·3H2O, in facilitating a remarkable switch in mechanism from a homogeneous to heterogeneous catalytic manifold. Evidence for heterogeneity includes sigmoidal kinetic traces, an order in Pd of 0.26 and catalyst turnover sequestration upon addition of excess Hg. The TOF and TON values recorded using K4[Fe(CN)6] (<220 ppm H2O) were higher than when using K4[Fe(CN)6]·3H2O (>4000 ppm H2O). Catalytic cycles are configured according to the experimental evidence gained from this study. We conclude that water plays a critical role in Pd catalyst speciation in arylcyanation chemistry.

UR - http://www.scopus.com/inward/record.url?scp=85058890301&partnerID=8YFLogxK

U2 - 10.1039/c8re00178b

DO - 10.1039/c8re00178b

M3 - Article

AN - SCOPUS:85058890301

SN - 2058-9883

VL - 4

SP - 122

EP - 130

JO - Reaction Chemistry & Engineering

JF - Reaction Chemistry & Engineering

IS - 1

ER -