Oxidative addition across Zr/Co multiple bonds in early/late heterobimetallic complexes

Abstract

The reactivity of heterobimetallic Zr/Co complexes linked by phosphinoamide ligands towards the oxidative addition of I(2) and alkyl halides is reported. These reactions are accompanied by dissociation of one phosphine ligand from Co and eta(2)-coordination to Zr. Addition of H(2) leads to both oxidative addition across the M-M bond and P-N bond cleavage.

A Catalytic Application of Co/Zr Heterobimetallic Complexes: Kumada Coupling of Unactivated Alkyl Halides with Alkyl Grignard Reagents

“…[20] We suspect that this difference can be attributed to both sterics and to the lesser stability of the methyl radical compared to other alkyl radicals. In support of this, in reactions between MeI and 5 in the presence of TEMPO, TEMPO-Me was not detected by GC-MS and the MeI addition product 6 was formed in high yield.…”

“…This is likely a result of both the less electron-rich nature of 1 as well as the difference in the nature and reactivity of the two-electron reduction products of 2 and 3. [20] This catalytic system shows unusual activity towards alkyl chlorides, although yields from reactions with alkyl iodide and bromide substrates are, in all cases, higher than the corresponding alkyl chlorides. While yields generally decrease in the order R-I, R-Br Ͼ R-Cl, these differences in yields are relatively minor in some cases.…”

“…[19] These species are highly reactive towards oxidative addition of small molecule substrates, including alkyl halides such as methyl iodide, cyclohexyl chloride, and 2-iodopropane to generate species such as (η 2 -MesNPiPr 2 )Zr-(MesNPiPr 2 ) 2 (μ-CH 3 )CoI (6) and {η 2 -PiPr 2 N[C 6 (CH 3 ) 2 H 2 -(CH 2 )]}Zr(MesNPiPr 2 ) 2 CoI (7). [20] Since alkyl halide activation is an important step in carbon-carbon bond-forming reactions, we have chosen to examine the catalytic performance of Zr/Co early/late heterobimetallic complexes in the cross-coupling reactions of alkyl halides with alkyl Grignard reagents (Kumada coupling). Herein we discuss the remarkable catalytic activity of these Zr/Co complexes compared to monometallic Co species, including activity towards alkyl chlorides.…”

Homo- and heteroleptic group 4 2-(diphenylphosphino)pyrrolide complexes: Synthesis, coordination chemistry and solution state dynamics

“…Thus, the extent of metal-metal bonding with first row transition metals is strongly dependent on the nature of the metal ions and metal coordination environment, rendering the bonding highly variable/tunable. Accordingly, Nagashima and Thomas have found that subtle variation of the electronic and steric properties of phosphinoamide ligand frameworks can drastically affect the structure and reactivity of mono-and bimetallic complexes [25][26][27][28][36][37][38][39][40][41][42][43][44][45]. Thus, we are interested in synthesizing trigonally symmetric heterobimetallic complexes of rigid, bifunctional hard/soft phosphinopyrrolide ligands to further the systematic study of metal-metal bonding and reactivity in P,N-bridged complexes.…”

“…In addition to the abovementioned ''Z-type'' bonding and reactivity, Thomas has observed Zr-Co multiple bonding that yields a diverse range of 1-and 2-electron processes that can result from direct or indirect reactivity of the metal-metal multiple bond: for example, CO 2 activation, hydrosilylation, E-H and E-E (E = N, O, S) bond activation [39][40][41][42][43][44][45]. Based on the plethora of chemistry available from a single class of early/late metal-metal multiple bonds, it is apparent that further investigation of these types of structures is warranted.…”