Exploring Trends in Metal–Metal Bonding, Spectroscopic Properties, and Conformational Flexibility in a Series of Heterobimetallic Ti/M and V/M Complexes (M = Fe, Co, Ni, and Cu)

Abstract

To understand the metal-metal bonding and conformational flexibility of first-row transition metal heterobimetallic complexes, a series of heterobimetallic Ti/M and V/M complexes (M = Fe, Co, Ni, and Cu) have been investigated. The titanium tris(phosphinoamide) precursors ClTi(XylNPPr) (1) and Ti(XylNPPr) (2) have been used to synthesize Ti/Fe (3), Ti/Ni (4, 4), and Ti/Cu (5) heterobimetallic complexes. A series of V/M (M = Fe (7), Co (8), Ni (9), and Cu (10)) complexes have been generated starting from the vanadium tris(phosphinoamide) precursor V(XylNPPr) (6). The new heterobimetallic complexes were characterized and studied by NMR spectroscopy, X-ray crystallography, electron paramagnetic resonance, and Mössbauer spectroscopy, where applicable, and computational methods (DFT). Compounds 3, 4, 7, and 8 are C-symmetric with three bridging phosphinoamide ligands, while compounds 9 and 10 adopt an asymmetric geometry with two bridging phosphinoamides and one phosphinoamide ligand bound η to vanadium. Compounds 4 and 5, on the other hand, are asymmetric in the solid state but show evidence for fluxional behavior in solution. A correlation is established between conformational flexibility and metal-metal bond order, which has important implications for the future reactivity of these and other heterobimetallic molecules.

Enhanced Fe-Centered Redox Flexibility in Fe–Ti Heterobimetallic Complexes

“…Two other Fe–Ti systems have been reported in the literature: Ti(μ-XylNP i Pr 2 ) 3 FeBr 27 and Ti(μ-NP) 3 Fe/K 2 [(κ 1 -NP)Ti(μ-NP) 2 Fe], 36 where Xyl is xylyl and NP is diphenylphosphinopyrrolide. Unfortunately, no CV data for these complexes were reported.…”

“…Previously, polarized triple bonds were predicted for related heterobimetallic complexes, where bond polarization increases as the different metals’ groups are further separated on the periodic table. 27,30,32 Also of interest is that the LUMO (2a 1 ) is similar across the series and has contributions from the Fe 4p, P 3s/3p, and Ti 3d z 2 orbitals. The Fe 4p and Ti 3d z2 contributions in the LUMO increase in the order of 2 red , 2 , and 2 ox , and hence are largest for the most oxidized Fe–Ti species, 2 ox .…”

“…A notable example is (THF)Zr(μ-MesNP i Pr 2 ) 3 Co(N 2 ), whose electronic structure is consistent with that of a Co –I Zr IV core based on K-edge XAS data. 35 Currently, we extend this concept to FeTi complexes, 27,30,36 where the large electronegativity difference between Fe (1.80) and Ti (1.38) should also engender highly polarized Fe–Ti bonds where the electron density is mostly localized at Fe. 37−40…”

Computational Approach to Molecular Catalysis by 3d Transition Metals: Challenges and Opportunities

“…394 DFT calculations were performed to elucidate the Ti−Co metal bond, as represented pictorially in Figure 10. 395−397 Experimental results were supported by computations that improve the understanding of the electronic structure of the catalytic species and specifically the nature of the Ti–Co interaction.…”

Selective Synthesis of a Series of Isostructural MIICuI Heterobimetallic Complexes Spontaneously Assembled by an Unsymmetrical Naphthyridine‐Based Ligand

“…[6][7][8][9][10] In particular, the synthesis of heterometallic complexes poses significant challenges since intricate, multidentate ligandso ften lack specificity in differentiating the binding of metals. [11] Theu se of bifunctionall igandsw ith hard and soft binding sites, including those based on different P, Nand N,N-chelation, [12,13] has been as uccessful strategy in this regard; [14][15][16][17][18] however,t his approach often resultsi ns tructures that do not allow ready access to bridging coordination sites, [16][17][18][19][20] or is specific to certainm etal-metal combinations. [21] Rigid, naphthyridine-based ligands are suitable candidates for addressing these issues.…”