Activation of B-H, Si-H, and C-F bonds with Tp′Rh(PMe₃) complexes: Kinetics, mechanism, and selectivity

TY - JOUR

T1 - Activation of B-H, Si-H, and C-F bonds with Tp′Rh(PMe3) complexes

T2 - Kinetics, mechanism, and selectivity

AU - Procacci, Barbara

AU - Jiao, Yunzhe

AU - Evans, Meagan E.

AU - Jones, William D.

AU - Perutz, Robin N.

AU - Whitwood, Adrian C.

N1 - © 2014 American Chemical Society. This is an open access article published under a Creative Commons Attribution (CC-BY) License, which permits unrestricted use, distribution and reproduction in any medium, provided the author and source are cited.

PY - 2015/1/28

Y1 - 2015/1/28

N2 - The photochemical reactions of Tp′Rh(PMe3)H2 (1) and thermal reactions of Tp′Rh(PMe3)(CH3)H (1a, Tp′ = tris(3,5-dimethylpyrazolyl)borate) with substrates containing B-H, Si-H, C-F, and C-H bonds are reported. Complexes 1 and 1a are known activators of C-H bonds, including those of alkanes. Kinetic studies of reactions with HBpin and PhSiH3 show that photodissociation of H2 from 1 occurs prior to substrate attack, whereas thermal reaction of 1a proceeds by bimolecular reaction with the substrate. Complete intramolecular selectivity for B-H over C-H activation of HBpin (pin = pinacolate) leading to Tp′ Rh-(PMe3)(Bpin)H is observed. Similarly, the reaction with Et2SiH2 shows a strong preference for Si-H over C-H activation, generating Tp′Rh-(PMe3)(SiEt2H)H. The Rh(Bpin)H and Rh(SiEt2H)H products were stable to heating in benzene in accord with DFT calculations that showed that reaction with benzene is endoergic. The intramolecular competition with PhSiH3 yields a ∼1:4 mixture of Tp′Rh(PMe3)(C6H4SiH3)H and Tp′Rh(PMe3)(SiPhH2)H, respectively. Reaction with pentafluoropyridine generates Tp′Rh(PMe3)(C5NF4)F, while reaction with 2,3,5,6-tetrafluoropyridine yields a mixture of C-H and C-F activated products. Hexa fluorobenzene proves unreactive. Crystal structures are reported for B-H, Si-H, and C-F activated products, but in the latter case a bifluoride complex Tp′Rh(PMe3)(C5NF4)(FHF) was crystallized. Intermolecular competition reactions were studied by photoreaction of 1 in C6F6 with benzene and another substrate (HBpin, PhSiH3, or pentafluoropyridine) employing in situ laser photolysis in the NMR probe, resulting in a wide-ranging map of kinetic selectivities. The mechanisms of intramolecular and intermolecular selection are analyzed. (Chemical Equation Presented).

AB - The photochemical reactions of Tp′Rh(PMe3)H2 (1) and thermal reactions of Tp′Rh(PMe3)(CH3)H (1a, Tp′ = tris(3,5-dimethylpyrazolyl)borate) with substrates containing B-H, Si-H, C-F, and C-H bonds are reported. Complexes 1 and 1a are known activators of C-H bonds, including those of alkanes. Kinetic studies of reactions with HBpin and PhSiH3 show that photodissociation of H2 from 1 occurs prior to substrate attack, whereas thermal reaction of 1a proceeds by bimolecular reaction with the substrate. Complete intramolecular selectivity for B-H over C-H activation of HBpin (pin = pinacolate) leading to Tp′ Rh-(PMe3)(Bpin)H is observed. Similarly, the reaction with Et2SiH2 shows a strong preference for Si-H over C-H activation, generating Tp′Rh-(PMe3)(SiEt2H)H. The Rh(Bpin)H and Rh(SiEt2H)H products were stable to heating in benzene in accord with DFT calculations that showed that reaction with benzene is endoergic. The intramolecular competition with PhSiH3 yields a ∼1:4 mixture of Tp′Rh(PMe3)(C6H4SiH3)H and Tp′Rh(PMe3)(SiPhH2)H, respectively. Reaction with pentafluoropyridine generates Tp′Rh(PMe3)(C5NF4)F, while reaction with 2,3,5,6-tetrafluoropyridine yields a mixture of C-H and C-F activated products. Hexa fluorobenzene proves unreactive. Crystal structures are reported for B-H, Si-H, and C-F activated products, but in the latter case a bifluoride complex Tp′Rh(PMe3)(C5NF4)(FHF) was crystallized. Intermolecular competition reactions were studied by photoreaction of 1 in C6F6 with benzene and another substrate (HBpin, PhSiH3, or pentafluoropyridine) employing in situ laser photolysis in the NMR probe, resulting in a wide-ranging map of kinetic selectivities. The mechanisms of intramolecular and intermolecular selection are analyzed. (Chemical Equation Presented).

UR - http://www.scopus.com/inward/record.url?scp=84921838827&partnerID=8YFLogxK

U2 - 10.1021/ja5113172

DO - 10.1021/ja5113172

M3 - Article

SN - 0002-7863

VL - 137

SP - 1258

EP - 1272

JO - Journal of the American Chemical Society

JF - Journal of the American Chemical Society

IS - 3

ER -