Steric and Electronic Effects in the Formation and Carbon Disulfide Reactivity of Dinuclear Nickel Complexes Supported by Bis(iminopyridine) Ligands

Abstract

We are developing bimetallic platforms for the cooperative activation of heteroallenes. Toward this goal, we designed a new family of bis(iminopyridine) ((N,N′-1,1′-(1,4-phenylene)bis(N-(pyridin-2-ylmethylene)methanamine) and N,N′-1,1′-(1,4-phenylene)bis(N-(1-(pyridin-2-yl)ethylidene)methanamine)) dinickel complexes, synthesized their CS2 compounds, and studied their reactivity. Bis(iminopyridine) ligands L react with Ni(COD)2 to form Ni2(L)2 complexes or Ni2(L)(COD)2 complexes as a function of the steric and electronic properties of the ligand precursor. Product structures disclosed an anti geometry in the Ni2(L)(COD)2 species and helical (anti) structures for Ni2(L)2 complexes. Carbon disulfide adducts Ni2(L)(CS2)2 were obtained in good yields upon addition of CS2 to Ni2(L)(COD)2 or in a one-pot reaction of L with 2 equiv of both Ni(COD)2 and CS2. Ni2(L)(CS2)2 complexes are highly flexible, displaying both syn and anti conformations (shortest S- - -S separations of 5.0 and 9.5 Å, respectively) in the solid state. DFT calculations demonstrate virtually no energy difference between the two conformations. Electrochemical studies of the Ni2(L)(CS2)2 complexes displayed two ligand-based reductions and a broad CS2-based oxidation. Chemical oxidation with [FeCp2]+ liberated free CS2. The addition of NHC (NHC = 1,3-di-tert-butylimidazolin-2-ylidene) to Ni2(L)(CS2)2 yielded Ni2(NHC)2(CS2)2, in which both carbon disulfide ligands are bridging two Ni centers.

Coordination Chemistry and Reactivity of Bis(aldimino)pyridine Nickel Complexes in Four Different Oxidation States

“…We have been exploring the coordination chemistry and reactivity of mononuclear and dinuclear complexes with iminopyridine ligands in the activation of small molecules, in particular CS 2 and CO 2 . We have previously reported that the bidentate iminopyridine ligand [NN] enables side-on coordination of CS 2 at square-planar Ni centers, Ni­[NN]­(η 2 -CS 2 ). , However, in spite of the significant elongation of the metal-bound C–S bond, no C–S bond breaking (or C–C bond formation) was observed.…”

Cleavage of Carbon Disulfide by n‐Propyldiphenylphosphine and Nickel(II) Bromide

“…The geometry of the Ni{η 2 ‐SC(P n PrPh 2 ) 2 } unit can be compared to the structures of previously studied nickel complexes of carbon disulfide, Ni(η 2 ‐CS 2 )(dtbpe) (dtbpe=1,2‐bis(di‐ tert ‐butyl‐phosphino)ethane and Ni(η 2 ‐CS 2 )(P‐alkenephosphor‐amidite) 2 . In Ni(η 2 ‐CS 2 )(dtbpe) these distances are: Ni−S, 2.147(2) Å; Ni−C, 1.922(5) Å, C−S, 1.732(6) Å . In Ni( η 2 ‐CS 2 )(P‐alkene phosphoramidite) 2 they are: Ni−S, 2.1529(8) Å; Ni−C, 1.913(3) Å; S−C, 1.685(3) Å .…”

“…[33] In Ni(h 2 -CS 2 )(dtbpe) these distances are:N i ÀS, 2.147(2) ;N i ÀC, 1.922(5) ,C ÀS, 1.732 (6) . [29,32] In Ni(h 2 -CS 2 )(P-alkene phosphoramidite) 2 they are:N i ÀS, 2.1529 (8) ;N i ÀC, 1.913(3) ;S ÀC, 1.685(3) . [33] There is ap articularlys trong similarity in the h 2 -CSNi units in [Ni{h 2 -SC(P n PrPh 2 ) 2 }Br(P n PrPh 2 )]Br·0.5CS 2 (1)a nd in Ni(h 2 -CS 2 )(dtbpe).…”

“…For example, ar eaction between Ni(CO) 2 (PPh 3 ) 2 and carbon disulfide yields ac omplex with an empirical formula Ni(CS 2 )(PPh 3 ), while the reaction between Ni(COD) (COD = cyclooctadiene), at ertiary phosphine, and carbon disulfidey ields ad imeric complexw ith the same general composition as described in reaction (5). [27][28][29]…”

Activation of heteroallenes by coordinatively unsaturated nickel(ii) alkyl complexes supported by the hydrotris(3-phenyl-5-methyl)pyrazolyl borate (TpPh,Me) ligand

“…[8][9][10][11][12][13][14][15][16][17][18] Further transformations of these substrates can be achieved via cleavage of the carbon-sulfur bond, similar to sulfur abstraction observed in low valent transition metal complexes. 34,35 Based on our interest in utilizing reactive metal-carbon bonds for activation of small molecules, [36][37][38][39][40][41][42] we investigated reactions of sulfur containing heteroallenes toward coordinatively unsaturated hydrotris( pyrazolyl)borate nickel(II) alkyl complexes. [22][23][24][25][26][27][28][29] The carbon-sulfur bonds in CS 2 are less susceptible to metal-mediated cleavage, [30][31][32][33] however, and the reactivity of the insertion products is a function of their structures.…”