Triple C–H Bond Activation of a Nickel-Bound Methyl Group: Synthesis and X-Ray Structure of a Carbide Cluster (NiCp)₆(μ₆-C)

Abstract

A new hexanuclear cyclopentadienylnickel carbide cluster (NiCp)(6)(μ(6)-C) (1) was obtained through the thermolysis of the alkene complex [NiCp(CH(3))(η(2)-CH(2)═CHC(4)H(9))] (4). The X-ray molecular structure of 1 (monoclinic; P2(1)/c; Ni-C(carbide) = 1.767(4)-2.109(4) Å) reveals a highly deformed octahedral arrangement of nickel atoms with two octahedron edges opened (Ni-Ni bonding distances = 2.410(1)-2.623(1) Å, Ni···Ni nonbonding distances = 3.107(2) and 3.108(2) Å). Cluster 1 is the first example of a homoleptic, cyclopentadienylnickel carbide cluster. Moreover, (13)C-labeling studies proved that the carbido ligand in cluster 1 originated from the Ni-bound methyl group. This transformation requires a triple C-H bond activation in the methyl group, which has not been observed so far for late transition metal compounds.

Mechanistic Insight into H/D Exchange by a Pentanuclear Ni–H Cluster and Synthesis and Characterization of Structural Analogues of Potential Intermediates

“…Cyclopentadienyl complexes are well documented in the organometallic chemistry of Ni and have also found use as a supporting ligand in Ni clusters . Of interest in H/D exchange with 1 is that the formally anionic (η 5 -Cp)­( i Pr 3 P) 4 Ni 5 (μ 2 -H) 4 – fragment in 3 is isoelectronic to the proposed intermediate for H/D exchange via the H 2 dissociation mechanism, (η 6 -C 6 D 6 )­Ni­[( i Pr 3 P)­Ni] 4 (μ 2 -H) 4 .…”

“…Thousands of transition metal clusters have been reported in the Cambridge Structure Database with the vast majority of them composed of either late transition metals with π-acceptor ligands like CO or early transition metals with π-donor ligands . Few examples of clusters are known that are composed of solely late transition metals and electron-rich phosphines and hydrides. − Our group has reported examples of inert-bond activation by the electron-deficient pentanuclear Ni cluster, [( i Pr 3 P)­Ni] 5 H 6 ( 1 ), which includes ultra-deep hydrodesulfurization (HDS), CC bond cleavage of unactivated alkenes, and catalytic H/D exchange of unactivated aromatics such as benzene (Scheme ). Moreover, these transformations all proceed at room temperature.…”

Methyl Complexes of the Transition Metals

“…TM−CH 3 complexes can rearrange by reversible α‐hydrogen elimination and formation of (H)TM=CH 2 species (Scheme d) . In an intriguing example, α‐hydrogen elimination of transiently formed [CpNi‐CH 3 ] is proposed as the first C−H activation step in a tandem process that leads to the formation of the unprecedented carbide cluster [(CpNi) 6 (μ 6 ‐C)] ( 3.29 ) (Scheme d) …”

Peraurated nickel carbide carbonyl clusters: the cationic [Ni6(C)(CO)8(AuPPh3)8]2+monocarbide and the [Ni12(C)(C2)(CO)17(AuPPh3)3]−anion containing one carbide and one acetylide unit

“…20 and Ni 6 (C)(Cp) 6 ,24 of an octahedral Ni-mono-carbide cluster.The[PPh 3 Au-AuPPh 3 ] 2+ fragments are μ 3 -bonded to two contiguous triangular faces of the Ni 6 -octahedron, with one Au forming three Ni-Au bonds and the other only two [Ni-Au 2.601(2)-2.8561(8) Å, average 2.672(8) Å]. The sixth Au⋯Ni contact [3.404(1) Å] is essentially non-bonding; for comparison, the sum of the covalent and van der Waals radii of Ni and Au are 2.86 and 3.29 Å, respectively.…”