Dismantling of Vinyl Ethers by Pentanuclear [(iPr3P)Ni]5H6: Facile Cooperative C?O, C?C and C?H Activation Pathways

Article abstract of DOI:10.1002/chem.201803451

The [(iPr₃P)Ni]₅H₆ cluster (1) and H₂C=CHOtBu react at room temperature to form the new pentanuclear NiH carbide [(iPr₃P)Ni]₅H₄(C)(CO) (3), along with an equivalent of isobutylene. This transformation requires the activation of multiple unreactive bonds, including C?H, C?C, and C(sp³)?O bond cleavage. Analysis of the reaction mixture by ¹H NMR revealed the production of two additional paramagnetic species, assigned as [(iPr₃P)Ni]₄H₄(C-CH₃)NiOtBu (4 a) and [(iPr₃P)Ni]₄H₄(C-CH₂OtBu)NiOtBu (5 a), which arise from C(sp²)?O bond cleavage and CH bond rearrangements. The reaction of 1 with H₂C=CHOSiMe₂CH₂Ph produced the isolable 4 a analogue [(iPr₃P)₄Ni₅]H₄(CCH₃)(OSiMe₂CH₂Ph) (4 c). An isolable analogue of 5 a was obtained from the reaction of 1 with H₂C=CHOAd (Ad=1-admantyl), which produced [(iPr₃P)₄Ni₅]H₄(CCH₂OAd)(OAd) (5 d). The utilization of both cluster faces and vertices for bonding substrate fragments in these transformations demonstrates the remarkable flexibility of the robust Ni₅H₄ core in the cooperative activation of multiple C?O, C?C and C?H bonds.

Full text of DOI:10.1002/chem.201803451

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Accepted Article
Title: Dismantling of Vinyl Ethers by Pentanuclear [(iPr3P)Ni]5H6:
Facile Cooperative CO, CC and CH Activation Pathways
Authors: Manar M. Shoshani, Volodymyr Semeniuchenko, and Samuel
A. Johnson
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10.1002/chem.201803451
Chemistry - A European Journal
Dismantling of Vinyl Ethers by Pentanuclear
[(iPr3P)Ni]5H6: Facile Cooperative CO, CC and
CH Activation Pathways
Manar M. Shoshani, Volodymyr Semeniuchenko, and Samuel A. Johnson*
Department of Chemistry and Biochemistry, University of Windsor
Sunset Avenue 401, Windsor, ON, N9B 3P4, (Canada)
Fax: (+1) 519-973-7098
E-mail: sjohnson@uwindsor.ca
1
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10.1002/chem.201803451
Chemistry - A European Journal
Abstract
The [(iPr3P)Ni]5H6 cluster (1) and H2C=CHOtBu react at room-temperature to form the new
pentanuclear Ni-H carbide [(iPr3P)Ni]5H4(C)(CO) (3), along with an equivalent of
isobutylene. This transformation requires the activation of multiple unreactive bonds,
1
including CH, CC, and C(sp3)O bond cleavage. Analysis of the reaction mixture by H
NMR revealed the production of two additional paramagnetic species, assigned as
[(iPr3P)Ni]4H4(C-CH3)NiOtBu (4a) and [(iPr3P)Ni]4H4(C-CH2OtBu)NiOtBu (5a), which
arise from C(sp2)O bond cleavage and CH bond rearrangements. The reaction of 1 with
H2C=CHOSiMe2CH2Ph produced the isolable 4a analogue [(iPr3P)4Ni5]H4(C-CH3)(O-
SiMe2CH2Ph) (4c). An isolable analogue of 5a was obtained from the reaction of 1 with
H2C=CHOAd (Ad =1-admantyl), which produced [(iPr3P)4Ni5]H4(C-CH2OAd)(OAd)
(5d). The utilization of both cluster faces and vertices for bonding substrate fragments in
these transformations demonstrates the remarkable flexibility of the robust Ni5H4 core in
the cooperative activation of multiple C-O, C-C and C-H bonds.
Introduction
Despite recent progress in the activation of both CC1 and CO2-3 bonds, large
thermodynamic barriers in transition metal-mediated functionalization hinder further
advancement. These bonds have garnered interest due to their presence in crude oil
distillates and potential biofuels such as lignin.4-5 The opportunity to use these abundant
materials as low-cost chemical feedstocks has led to significant progress in transition
metal-mediated CO bond activation,2, 6-23 as well as the microscopic reverse, CO bond
formation.24-29 Cooperative reactivity between multiple proximal transition metal centres
in clusters provides a strategy towards bond activation and functionalization,30 reminiscent
2
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10.1002/chem.201803451
Chemistry - A European Journal
of surface chemistry or polymetallic enzymes. Although transition metal clusters are
plentiful, highly reactive clusters capable of difficult bond transformations remain an
emerging field.31-39 Late transition metal clusters are generally supported by π-acceptor
ligands,40 or multi-electron bridging donor ligands such as sulfides.41 The combination of
only late transition metal centres and electron-rich ligands such as alkylphosphines and
hydrides is a rare combination for polynuclear species.42-46
We have recently demonstrated the ability of the electron-deficient cluster
[(iPr3P)Ni]5H6 (1) to selectively abstract a carbon atom from unactivated alkenes and
rearrange C-H bonds to give the carbide cluster [(iPr3P)Ni]5H4(µ5-C)(2) under very mild
conditions, as shown in Scheme 1a, despite its lack of reactivity with a number of
functional groups and typically reactive small molecules.39 The reaction ethylene with
proceeds selectively at –30 °C, even in the presence of added ketones, alcohols, amines,
esters, amides alkynes and alkyl halides. Isolated intermediates from the reaction of 1 with
isobutylene and styrene, shown in Scheme 1b, reveal a triple CH bond activation
mechanism that utilizes cooperative substrate binding to the Ni5 centres prior to CC bond
cleavage. In this paper, we describe reactions of 1 with alkoxy substituted alkenes via a
surprising variety in mechanistic manifolds that all involve facile inert-bond activations,
with rearrangement of C-H bonds and C-O bond activation.
3
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