Isocyanide complexes state

The isocyanide ligand, CNR, is formally isolobal with a carbene ligand. Several studies have investigated iron(Ill) porphyrin isocyanide complexes which have the general formula [FeCPorKCNR) ]. However, these studies have mostly been concerned with spin state and spectroscopic properties rather than chemical transformations and will not be discussed in detail here. Crystallographic details are given for two of the complexes. " ... 

No isocyanide complexes have been described for lower oxidation states, probably because the c-donating properties of this kind of ligand are too strong or the w-accepting properties too weak. 

Comparison between the half-wave potentials (equations 2 to 4) of [Cr(CNR)6](PF6)2, e.g. for R = Bu , -1.04, -0.28 and 0.84 V (versus SCE),22 with those for [Cr(CNPh)6](PF6)2, i.e. -0.35, 0.25 and 1.00 V,20 shows that alkyl and aryl isocyanides favour respectively the higher and the lower oxidation states as expected from the greater a-donor and weaker jr-acceptor capabilities of the alkyl over the aryl isocyanides. Similarly, the phosphines in the mixed ligand complexes (Table 3), 23 relative to isocyanide ligands, stabilize the Cr111 oxidation state. The great difference in the relative stabilities of Cr—C bonds in the cyano and phenyl isocyanide complexes is indicated by the magnitude of the shift (ca. 2.0 V) between the Cr(CN) "/Cr(CN)r (-1.130 V) and the Cr(CNPh)i+/Cr(CNPh)i+ reduction potentials.28... 

Cyanide and organic isocyanide complexes of chromium(ll) have been included with th lower oxidation states in Sections 35.2.1.1 and 35.2.1.2. 

Replacement of ligands in C3H5MoCl(CO)2(NCMe)2 by isocyanides has given the substituted products C3H5MoC1(CO)2(CNR)2 (R = alkyl) and C3H5MoC1(CO)(CNBu )3, and the reduced products [MoC1(CNBu )4]2 and m-Mo(CO)2(CNR)4 (R = Me, Et). No rationale for the loss of allyl and allyl chloride in the latter two cases was proposed (206). These reactions are rare examples of the formation of low-oxidation state metal-isocyanide complexes via reductive elimination of allyl or allyl chloride from metal-allyl species. The potential applications of mono-, bis-, and tris-n-allylic systems as precursors to low-oxidation state compounds remain to be explored. Substitution and simultaneous reduction of Mo(SBu )4 also occurred on reaction with CNBu to give Mo(SBu )2(CNBu )4 (207) (see Section IV,D,2). 

Activation of two Si—Si bonds in bis(disilanyl)alkanes with palladium(O) bis(tert-alkyl isocyanide) induced the formation of the cyclic bis(silyl)palladium(II) bis(terf-alkyl isocyanide) complexes (100) and disilanes described schematically in Scheme 42. These complexes were found to react with phenylacetylene, affording different amounts of five-membered cyclic products and acyclic products which are derived from the insertion of the alkyne into the general intermediate complex 101 (Scheme 42, equation 54). The bis(silanyl)dithiane palladium complex (102) was isolated and characterized in the solid state the two silicon atoms, the two isocyano carbons and the palladium atom are nearly in a plane with a short cross-ring Si—Si distance of 2.613(2) A, suggesting the possibility of covalently bonded two Si—Si atoms in the four-membered ring. Similar reaction with cyclic disilanes afforded oligomers, and cyclic 20-membered compounds have been prepared in the presence of nitriles248,249. 

Among the isocyanide complexes, Ru(bpy) (CNMe)42+ stands out as a remarkable Ru(II) polypyridine photosensitizer in view of (i) its long lifetime in fluid solution, and (ii) its very high excited-state oxidizing power ( e1/2 red v vs SCE)... 

Isocyanides (RNC) are better a donors and poorer xr acceptors than CO, as indicated by the observation that typical homoleptic isonitrile complexes of many metals are in higher oxidation states than the typical carbonyl complexes of the same metal. Some metal isocyanide complexes are given in Table 7-4. It should be pointed out that there are no carbonyl analogues of those compounds in the higher oxidation... 

Many of the Tc complexes (16, 17, 19) present the 0x0 Tc =0 + core and are pentacoordinate (square pyramid), but other metal oxidation states and coordination numbers are possible, for instance, in (20) (hexacoordinate with the dioxo Tc 02 " core), in (18) (heptacoordinateTc ), in (21) or (23) (hexacoordinate Tc ), or in (22) (hexacoordinate Tc ). In Tc-diphosphonate radiopharmaceuticals, used as bone imaging agents, the metal is beheved to be in the 4-4 oxidation states. The +1 oxidation state in the homoleptic isocyanide complex (22) is expected to be advantageous in terms of the kinetic inertness associated to its low-spin configuration,... 

A report has appeared of the results of energy-transfer and electron-transfer quenching experiments involving the A2 excited state of some binuclear rhodium isocyanide complexes, e.g. [Rh2(br)4], where br = 1,3-di-isocyanopropane, and [Rh2(TMB)4] , and TMB = 2,5-dimethyl-2,5-di-isocyanohexane. Detailed... 

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