Xenophilic Complexes Bearing a Tp^R Ligand, [Tp^RMM′L_n] [Tp^R=Tp, Tp^# (Tp); M=Ni, Co, Fe, Mn; M′L_n=Co(CO)₄, Co(CO)₃(PPh₃), RuCp(CO)₂]: The Two Metal Centers are Held Together not by Covalent Interaction but by Electrostatic Attraction

Abstract

A series of dinuclear complexes, [Tp(R)M--M'L(n)] [Tp(iPr(2) )M--Co(CO)(4) (1; M=Ni, Co, Fe, Mn); Tp(#)M--Co(CO)(4) (1'; M=Ni, Co); Tp(#)Ni--RuCp(CO)(2) (3')] (Tp(iPr(2) )=hydrotris(3,5-diisopropylpyrazolyl)borato; Tp(#) (Tp(Me(2),4-Br))=hydrotris(3,5-dimethyl-4-bromopyrazolyl)borato), has been prepared by treatment of the cationic complexes [Tp(iPr(2) )M(NCMe)(3)]PF(6) or the halo complexes [Tp(#)M--X] with the appropriate metalates. Spectroscopic and crystallographic characterization of 1-3' reveals that the tetrahedral, high-spin Tp(R)M fragment and the coordinatively saturated carbonyl-metal fragment (M'L(n)) are connected only by a metal-metal interaction and, thus, the dinuclear complexes belong to a unique class of xenophilic complexes. The metal-metal interaction in the xenophilic complexes is polarized, as revealed by their nu(CO) vibrations and structural features, which fall between those of reference complexes: covalently bonded species [R--M'L(n)] and ionic species [M'L(n)](-). Unrestricted DFT calculations for the model complexes [Tp(H(2) )Ni--Co(CO)(4)], [Tp(H(2) )Ni--Co(CO)(3)(PH(3))], and [Tp(H(2) )Ni--RuCp(CO)(2)] prove that the two metal centers are held together not by covalent interactions, but by electrostatic attractions. In other words, the obtained xenophilic complexes can be regarded as carbonylmetalates, in which the cationic counterpart interacts with the metal center rather than the oxygen atom of the carbonyl ligand. The xenophilic complexes show divergent reactivity dependent on the properties of donor molecules. Hard (N and O donors) and soft donors (P and C donors) attack the Tp(R)M part and the ML(n) moiety, respectively. The selectivity has been interpreted in terms of the hard-soft theory, and the reactions of the high-spin species 1-3' with singlet donor molecules should involve a spin-crossover process.

Crystal structure of tricarbonyl(N-diphenylphosphanyl-N,N′-diisopropyl-P-phenylphosphonous diamide-κ2P,P′)cobalt(I) tetracarbonylcobaltate(−I) toluene 0.25-solvate

“…For a similar, carbonyl-bridged dinuclear cobalt complex with this PNPNH ligand, see: Hansen et al (2013). Examples for structural reports of other Co I -Co ÀI ion-pair complexes can be found in Fellmann et al (1983), Bockman & Kochi (1989), Zhang et al (1994), Uehara et al (2005), van Rensburg et al (2007) and Azhakar et al (2012). Other transition metal complexes with this ligand are described in Aluri et al (2010) and Dulai et al (2011).…”

Synthesis and Characterization of Heteromultinuclear Ni/M Clusters (M = Fe, Ru, W) Including a Paramagnetic (NHC)Ni–WCp*(CO)3 Heterobinuclear Complex

“…The analogous NiRu 2 complex 3 is isostructural, with bent Ni–Ru–Ru (57.916(11) and 57.304(12)°) and Ru–Ni–Ru (64.780(12)°) angles along with significantly bent C NHC –Ni–Ru angles (142.56(8) and 151.81(8)°). The Ni–Ru distances (2.5165(5) and 2.5337(4) Å) are close to the Ni–Ru single-bond distance in Tp # Ni-RuCp­(CO) 2 (2.512(1) Å; Tp # = hydrotris­(3,5-dimethyl-4-bromopyrazolyl)­borato)), and the Ru–Ru bond distance (2.7053(5) Å) is in the range of a Ru–Ru single bond (2.59–2.75 Å) in some Ru cluster cases . Previously, similar structures of related MoNi 2 clusters supported by NHCs have been reported by Chetcuti .…”

Exchange coupling through diamagnetic [Fe(CO)4]2−bridging ligands in a xenophilic cluster

“…More recently, Akita and co-workers have reported the closely related xenophilic bimetallic complex Tp iPr2 Mn-Co(CO) 4 (Scheme 1d), along with its Fe, Co and Ni analogues, and argued that the interaction between metal centres is largely electrostatic, with only a very minor contribution from the direct overlap of the d orbitals on adjacent metals. 11 In this sense, the [Co(CO) 4 ]fragment acts as a diamagnetic ligand, completing the tetrahedral coordination sphere about the manganese centre. The key difference between these two bonding models lies in the population of the Mn-M antibonding orbitals: in our earlier model (Xu and Lin 10 ), they are vacant (as in typical organometallic clusters), while in the Akita model, 11 they would be singly-occupied, as in typical exchangecoupled clusters of high-spin Mn II .…”

“…11 In this sense, the [Co(CO) 4 ]fragment acts as a diamagnetic ligand, completing the tetrahedral coordination sphere about the manganese centre. The key difference between these two bonding models lies in the population of the Mn-M antibonding orbitals: in our earlier model (Xu and Lin 10 ), they are vacant (as in typical organometallic clusters), while in the Akita model, 11 they would be singly-occupied, as in typical exchangecoupled clusters of high-spin Mn II . The contrast between these two models has encouraged us to reassess the electronic structure of Mn 2 (thf) 4 (Fe(CO) 4 ) 2 , which is the subject of this paper.…”