Transition Metal Nitrosyl Compounds

In recent years transition metal nitrosyl compounds have attracted considerable interest, and several review articles have been published 1-11). This interest has been directed towards three main areas. 

Although a large number of transition metal nitrosyl compounds have been prepared 208), Mn3(77--Cp)3(NO)4 described in Section II, D is the only characterized nitrosyl cluster 130). King has isolated a compound for which he postulated the formula Fe2(NO)2[S2C2(CF3)2]2, but the mass spectra indicated the formulation Fe3(NO)4S[S2C2(CF3)2]2 240). 

Coppens P, Novozhilova I, Kovalevsky A (2002) Photoinduced linkage israners of transition-metal nitrosyl compounds and related complexes. Chem Rev 102 861-884... 

Nuclear quadrupole resonance spectroscopy, see also specific compounds cyclophosphazenes, 21 93 of subvalent compounds, 29 298, 308-309 transition metal nitrosyl complexes, 34 313-314... 

Reductive nitrosylation, transition metal nitrosyl complexes, 34 296-297 ReFejSj cluster, 38 41-43 self-assembly system, 38 41-42 Refining, of actinide metals, see Actinide, metals, purification Refractory compounds heat treatment of solids, 17 105-110 crystal growth, 17 105, 106 decomposition, 17 107,-110 spheroidization, 17 106, 107 preparation of, using radio-frequency plasma, 17 99-102... 

Dichlorodinitrosylmolybdenum and tungsten have been prepared by the reaction of the appropriate hexacarbonyl with nitrosyl chloride in dichloromethane.1 The corresponding dibromo derivatives have been prepared by a similar reaction with nitrosyl bromide.2 These are the only synthetic routes to these compounds they are rapid (3 hours) and convenient. The corresponding chromium compounds are unknown. This method is a general route to transition-metal nitrosyl halide... 

Reductive nitrosylation also occurs on reaction of hydroxylamine with transition metal oxo- compounds (33-35) ... 

No N nuclear quadrupole resonance (NQR) studies have been reported for transition metal nitrosyl complexes. This technique is expected to show interesting differences between linear and bent nitro-syls since the values of the quadrupole coupling constant and the asymmetry parameter depend on the relative populations of the nitrogen s,p, py, andpz orbitals. NQR spectroscopy has been used to study organic and inorganic nitroso compounds, and it is found that both... 

The complexes reported below are convenient precursors of a variety of transition metal nitrosyl complexes.5 Since all these compounds and intermediates are more or less air sensitive, operations should be carried out using standard inert atmosphere techniques.6 All the solvents must be purified and deoxygenated prior to use. 

The NO+ ion is isoelectronic with CO, and, like CO, will form bonds to metals. Thus, for example, analogous to nickel carbonyl, Ni(CO)4, there is the isoelectronic Co(CO)3NO. These transition-metal nitrosyl complexes are discussed in Section 22-12, but we may note here that the compound responsible for the brown ring in the test for nitrates is a nitrosyl complex of iron with the formula [Fe(H20)5N0]2 +. ... 

As mentioned before, we have studied in our group various types of insertion reactions with phosphine substituted transition metal nitrosyl hydrides [37]. In general, these compounds appear to have a very hydridic bond, but also... 

Transition metal compounds containing nitric oxide as a coordinated ligand are normally called nitrosyl complexes. However, the term nitrosyl , is only sometimes restricted specifically to complexes which can be regarded as containing a three-electron metal-nitric oxide bond, and the term seems to be used generally for all nitric oxide compounds. Although there are many transition metal-nitrosyl complexes, relatively few also contain metal-carbon linkages and therefore fall within the subject of this chapter. 

The general topic of transition metal nitrosyl chemistry has been ably treated by Johnson and McCleverty (48), and this more restricted survey owes much to that review. Here we shall briefly consider the nature of the metal-ligand link in organometallic nitrosyls, the preparative chemistry of the main classes of compounds, and the physical data which have been derived for them, laying particular stress on the more recent developments. 

Many transition metal nitrosyl complexes release NO upon photolysis. For example, NO release was observed from Mo(CO)(NO)(dppe)(dtc), where dtc = S2CNMe2, and dppe = diphenyl-phosphino-ethane. The lowest energy absorption band of this compound, at 520 nm, has been assigned to a LLCT (dtc NO ) transition. Photolysis into the low energy side of this band (2irr = 546 nm) in benzene solutions results in loss of NO ((/> = 0.0018) [84]. 

Nitric oxide rapidly reacts with transition metals, which have stable oxidation states differing by one electron (see Chapters 2 and 3). Nitric oxide is unusual in that it reacts with both the ferric (Fe " ) and ferrous forms (Fe " ) of iron. TTie unpaired electron of nitric oxide is partially transferred to the metal forming a principally ionic bond. Complexes of ferric iron with nitric oxide are called nitrosyl compounds and will nitrosate (add an NO group) many compounds, while reducing the iron to the ferrous state (Wade and Castro, 1990). 

The 18-electron rale is not obeyed as consistently by these types of oiganome-tank compounds a by the carbonyl and nitrosyl complexes and their derivatives. For example, in addition to ferrocene. M(i 5-CsHs)2 compounds are known for most of the other elements of the first transition series (M — V, Cr, Mn.Co, Ni) and these cannot obey ihe 18-electron rule. However, only ferrocene shows exceptional thermal stability (stable to 500 C) and is not oxidized by air. Furthermore, cobaltocene, a 19-electron species, is readily oxidized to the 18-electron cobaltocenium ion. (Co(ip-CsH )3)4 , which reflects much of the thermal stability of ferrocene. Mixed cyclopentadienyl carbonyl complexes are common K -CjHjMCO) ]. [(if-CjH )-Cr(CO), . [( -CjHOMnCCOjJ, [(>r-C,H,>Fe(CO ,, . [fo -CjiyCoCoy. and (ip-CsH,)Ni(CO) 2. Of interest is the fact that among these compounds, the odd-atomic-number elements (V. Mn, and Co) form monomers and the even-atomic-number elements (Cr. Fe. and Ni) Ibrm dimers, which is in direct contrast to the behavior shown by the simple carbonyl complexes. Cyclopentadienyl derivatives are now known for every main group and transition metal of the periodic table and for most of the -block metals.89... 

The adsorption of nitric oxide is of further interest from the point of view of metal-nitrosyl interactions in inorganic chemistry. The bonding of nitrosyl ligands to transition metal centers in metal compounds has indicated that the NO ligand is amphoteric, i.e., it can be formally considered as N0+ or NO-(linear or bent) when bonding to a single metal center (16,17). 

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