Homoleptic complexes nickel

Schrauzer s Early Studies on Homoleptic Olefin Nickel(O) Complexes... 

With toluene solvated nickel atoms, the stannylenes Sn[CH(SiMe3)2]2 and Sn(C6H-2-f-Bu-3, 4, 5-Me3)2 at —78°C form homoleptic stannylene analogs of nickel tetracarbonyl, Ni(SnR2)4 with R = CH(SiMe3)2 and 2,3,4-Me3-6-f-BuC6H. The four membered cyclic stannylene Sn(NBu-t)2SiMe2 can also form a similar homoleptic complex. ... 

Shen and coworkers used Kawaguchi s phenoxy functionalised carbene ligand for the preparation of nickel(II) [62] and iron (II) [63] carbene complexes. Using the same deprotonation method — NaN(SiMe3)2— they attempted the synthesis of a mono-carbene nickel(II) complex that resulted in the formation of the homoleptic complex instead [62] (see Figure 4.16). Use of the correct stoichiometries significantly increased the yield. 

Ketz et al. synthesised a keto functionalised imidazolium salt using the standard protocol by reacting the appropriate N-aryl substituted imidazole with the respective keto halide [95], Their intention was to use the corresponding nickel(II) carbene enolate complex in olefin polymerisation reactions similar to the phosphino enolates in the SHOP process [1 ]. It proved difficult to prepare the intended precatalyst with only one carbene enolate ligand attached to the nickel centre. Initially, the homoleptic complex with two carbene enolate ligands was formed. The authors pointed out that the high proportion of n-olefins is unusual. 

Carboxylic acid amide functionalised imidazolium salts can be reacted with group 10 halides directly in the presence of an inorganic base (e.g. K COj) to form homoleptic complexes (see Figure 4.41) [122]. Interestingly, the carbene units are cis to each other and not trans as would be expected (see Figures 4.30 and 4.38). The cis complexation is not aided by hydrogen bonding as the carboxylic acid amide functionality loses its proton upon complexation to nickel. 

Atypical synthesis of naAed NHC-containing complexes has been reported by Cloke and coworkers. As shown in equation (7), the co-condensation of nickel, paUadium, and platinum vapor with the free NHC, TBu, provided two-coordinated homoleptic complexes of Ni(0), Pd(0), and Pt(0) (43). Unfortunately, in addition to the poor yield of the isolated product, this original methodology required a metal vapor synthesis apparatus. 

Nickel(II) complexes with two different dithiocarbamate ligands, [Ni(S2CNR2) (S2CNR2)], can be prepared via ligand exchange between pairs of homoleptic complexes (1484). These reactions have been followed HPLC activation parameters suggest an Sn2 mechanism. While the steric properties of the... 

The orange, air-stable, homoleptic tetrakis( 71-phosphabenzene)nickel (1046) is tetrahedral (point symmetry 54) and can be obtained from phosphabenzene and [Ni(cod)2].2 25 It features a short Ni—P bond length of 2.1274(5) A with considerable N i P 7r-backbonding and a i/(Ni—P) stretch at 168 cm-1. In solution, partial dissociation of one phosphabenzene ligand is observed. 2-Diphenylphosphino-3-methylphosphinine forms with [Ni(cod)2] in the presence of the CO the dinuclear complex (1047) with a W-frame structure.2526... 

In contrast to nickel, simple homoleptic Tpx or Bpx, and heteroleptic pyrazolylborate-halide complexes of palladium and platinum are largely unexplored. Indeed, while for 3d metals these are "standard" targets for each successive generation of poly(pyrazolyl)borate ligand, for the... 

In this work the ultrafast photophysical processes associated with photoinduced CO loss will be described with particular regard to the mononuclear homoleptic carbonyls Cr(CO)6, Fe(CO)5, and Ni(CO)4. These complexes were the earliest metal carbonyls to be synthesized, indeed Fe(CO)5 and Ni(CO)4 have been known since the latter part of the nineteenth century. The carbonylation of nickel provided an important route to high purity nickel which was required by many important industrial processes. However, it is only within the last few decades that adequate models have been developed to explain the mechanisms of photoinduced CO loss from metal carbonyl complexes. 

The group 8 (VIII) metals comprise almost 80% of the structurally characterized homoleptic bis(dithiolene) units. Nickel complexes alone account for... 

Some homoleptic unsymmetrical (dmit/mnt, dmit/tdas) dithiolene nickel complex-based D-A compounds with D = TTF and EDT-TTF also exhibit metal-like conductivity (see Table I) (101). Their molecular structure is shown in Scheme 3. The unsymmetrical tetraalkylammonium salts [MLjLJ- (M = Ni, Pd, Pt) have been prepared by ligand exchange reaction between tetraalkylammonium salts of MLj and ML21 (128, 129) and the D-A compounds have been synthesized by electrooxidation. Among these complexes, only the Ni derivatives exhibit metallic-like properties, namely, TTF[Ni(dmit)(mnt)] (metallic down to --30 K), a-EDT-TTF[Ni(dmit)(mnt)] (metallic down to 30 K), TTF[Ni(dmit)(tdas)] (metallic down to 4.2 K), and EDT-TTF[Ni(dmit)(tdas)] (metallic down to --50 K) (see Table I). The complex ot-EDT-TTF-[Ni(dmit)(mnt)J is isostructural (130) to a-EDT-TTF[Ni(dmit)2)] [ambient pressure superconductor, Section II.B.2 (124)]. Under pressure, conductivity measurements up to 18 kbar show a monotonous decrease of the resistivity but do not reveal any superconducting transition (101). 

Although several authors have reported on symmetrical and unsymmetrical homoleptic dithiolene complexes for third-order NLO applications (368, 436-440), the most complete and significant studies have been carried out by Underhill and co-workers (397, 431, 433, 434, 441-448). Two of these systems are shown in Scheme 25. One of the conclusions (434) is that an optimized material should absorb 800 nm (433) in order to have the highest ratio x(3 /a. For obtaining the material in a useful form, it is also proposed to embed the dithiolene complexes as guests in polymers such as poly(methylmethacrylate) (PMMA) (434, 449, 450). Along this line, the most efficient material in this series is the bis[l-butyl-2-phenylethene-l,2-dithiolato(2 )-S,S ]nickel(II) compound (29) shown in Scheme 25 (451). 

Figure 4.16 Synthesis of a homoleptic nickel(Il) carbene complex with a phenoxy functionalised NHC ligand.

Figure 4.41 Homoleptic nickel(ll) complex of a carboxylic acid amide functionalised carbene.

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