Cyanide and Isocyanide Complexes

4 Iron Carbonyl with Group 14 Ligands 6.01.4.1 Cyanide and Isocyanide Complexes 

Cyano-iron carbonyl complexes have received attention recently for their relationship to the active sites in hydro-genases. Some of this work will be discussed in the section on iron carbonyl complexes with thiolate ligands (see Section 6.01. 

Mononuclear Iron Carbonyls without Hydrocarbon Ligands 

A nitrogen-substituted iron carbonyl-cyanide complex 24 has been prepared from (Me3TACN)FeCl2 by adding cyanide ions in the presence of GO (Me3TAGN =iV,iV, A -trimethyl-l,4,7-triazacyclononane).  

Quantum calculations of equilibrium structures and vibrational frequencies of [Fe(CN) (CO)j,] (for the series 5C = 0-6, = 0-5, q = Z—x) as well as the Fe compounds (where x=l,y = 4, q = —l) and the Fe compounds (where x = 5, y=l, q=—2) are known/ The compounds were studied because of the relationship to the catalytic centers in hydrogenases. Calculated bond lengths agree with experimental values for the Fe-CO bonds (slightly shorter), but are longer than experimental for Fe-CN. The calculated vibrational frequencies were higher for CN and lower for CO than the experimental values. The expected correlation between the amount of TT-backdonation and the calculated vibrational mode of the CO was seen. The Fe — L ir-backdonation affects the stretching frequencies of CO more than those of CN. Finally, the Fe-CN bonds have less Tt-character than the Fe-CO bonds. 

---

The extensive organometallic chemistry of chromium, i.e. the hexacarbonyl and its derivatives, organochromium compounds without carbonyl ligands, cyanide and isocyanide complexes, alkene, allyl, diene, cyclopentadiene and arene derivatives, and complexes of a-donor carbon ligands, has been recorded in Chapters 26.1 and 26.2 of Volume 3 of Comprehensive Organometallic Chemistry .1 In the present section, chromium complexes... 

In this article the term organometallic compound includes alkyl and aryl derivatives of the rare earths—the transition metals of group III, scandium, yttrium, lanthanum and the lanthanides cerium to liitetium with covalent metal-to-carbon a-bonds, as well as the so-called 77-complexes with more than monohapto metal-to-carbon bonds, for example cyclopentadienyl and olefin complexes, metal acetylides, but not carbonyls, cyanides and isocyanide complexes. Derivatives of scandium, yttrium and lanthanum are included and discussed together with the compounds of the lanthanides, because of many similarities in the synthesis and the chemistry of these organometallic derivatives of the rare earths. 

Seven and eight coordinate molybdenum complexes and related molybaenum(IV) oxo complexes with cyanide and isocyanide ligands. S. J. Lippard, Prog. Inorg. Chem., 1976, 21, 91-103 (44). 

Iron carbonyl complexes with As, Sb, Bi donor ligands, 6, 57 with boron, 6, 7 cyanides and isocyanides, 6, 15 Fe3(CO)i2, 6, 260... 

Lippard, Stephen J., Seven and Eight Coordinate Molybdenum Complexes and Related Molybdenum (IV) Oxo Complexes, with Cyanide and Isocyanide... 

Cyanides.—A concise review of the seven- and eight-co-ordinate molybdenum complexes and related molybdenum(vi) 0x0 complexes, with cyanide and isocyanide ligands has appeared and Group Via cyanide complexes have been reviewed within the broader scope of transition metal cyanides. ... 

The problems (and the most interesting features) found in the spectroscopy of ionic metal cyanides and isocyanides occur because the CN ligand is nearly spherical. The CN ligand thus has a low barrier-internal rotation in M+CN" molecules. The equilibrium structure in the ground state can be linear cyanide, MCN, linear isocyanide, MNC, or even a T-shaped side-on complex (e.g., Na+N-)- The molecular geometry is evidently determined by... 

The computation of rotational constants Be from the inertia moments I corresponding to the interatomic distances in both types of comple.xes illustrates the situation clearly the cyanide and isocyanide isomers have rotational constants separated by about 0.6 GHz, and this shift upwards for the isocyanide species may be useful for their spectroscopic investigation, as already done for the pair of isomers MgNC and MgCN. Corresponding dipole moments are indicated in this connection. It should be added that the present values are consistent with the experimental parameter B = 4.358596 GHz assigned to a related complex FeCO [34]. 

One family of derivatives that will not be treated in this review, even though they contain metal-carbon bonds are carbonyl and cyanide (or isocyanide) complexes. These complexes are more relevant to coordination chemistry than organometalhc chemistry. 

ELECTROCHEMICAL GENERATION OF SUBSTRATE-BINDING SITES IN ORGANOMETALLIC COMPLEXES WITH THE M02( i-SR)n CORE. ELECTROSYNTHESIS OF CYANIDE AND ISOCYANIDE DERIVATIVES. 

EPR investigations are necessarily carried out in frozen solution at low temperature. Room temperature binding of thiols to FeMoco has been monitored by F NMR spectroscopy using /J-CF3C6H4S as the reporter ligand. These experiments revealed that the binding of thio-late is characterized by a dynamic equilibrium between the FeMoco and thiolate (159) and that cyanide and methyl isocyanide can bind to isolated FeMoco complexed with thiol (160). 

Silver(I) isocyanide complexes have been known for a long time and they were usually prepared by alkylation of silver cyanide.226 More recent reports include the study of steric effects of ligands... 

As a further illustration of the dependence of n i 7t pi-backbonding interactions on metal and ligand character, we may compare simple NiL complexes of nickel with carbonyl (CO), cyanide (CN-), and isocyanide (NC-) ligands, as shown in Fig. 4.41. This figure shows that the nNi 7rL pi-backbonding interaction decreases appreciably (from 28.5 kcal mol-1 in NiCO to 6.3 kcalmol-1 in NiNC-, estimated by second-order perturbation theory) as the polarity of the 7Tl acceptor shifts unfavorably away from the metal donor orbital. The interaction in NiCO is stronger than that in NiCN- partially due to the shorter Ni—C distance in the... 

---