Transition metal carbonyl nitrosyl compound

The research chemist likes to read not only about the specialized topics which interest him in detail, but also of the general chemical highlights of the preceding year. Since 1904, the Chemical Society s Annual Reports (B5) have covered, selectively, developments on an annual basis. Surveys of work on transition metal carbonyls and nitrosyls appeared at irregular intervals until 1955, after which time a new section on Transition Elements included an annual report on significant advances in this area. Five years later, a subdivision entitled Complexes included the work on organo-transition metal compounds. A new chapter, Transition Metal... 

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... 

This chapter is largely concerned with the structural chemistry of Fe, Co, Ni, Pd, and Pt, for the most part in finite complexes. The structures of the simpler compounds of these and other transition metals have been described under Halides, Oxides, etc. in the appropriate chapters. Other groups of compounds described in earlier chapters include hydrido compounds, oxo-, peroxo-, and superoxo-compounds, carbonyls, and nitrosyls, in Chapters 11, 12, and 18, respectively. We note here a few general points. 

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 +. ... 

The first transition metal complex containing four different substituents to be resolved was the manganese complex shown in Scheme 2, top [6,7]. In the cation of this complex, the Mn atom is surrounded by a cyclopentadienyl, a carbonyl, a nitrosyl, and a triphenylphosphine ligand. This complex can be prepared from the commercially available compound (C5H5)Mn(CO)3 in two steps yielding [(C5H5)Mn(CO)(NO)PPh3]PF6 as a racemate [8]. 

Metal nitrosyls are the transition metal complexes of nitric oxide (NO) containing a metal-nitrogen bond. Roussin s red salt, Na2[Fe2(NO)4S2], and Roussin s black salt, Na[Fe4(NO)7S3], were the earliest known metallic nitrosyls. In line with the inclusion of metal carbonyl complexes under the category of organometaUic compounds, the metallic nitrosyl complexes are also recently included in organometaUic compounds. The nitric oxide cation is isoelectronic with carbon monoxide. Hence, there is quite a bit of resemblance in the chemistry of metaUic carbonyls and nitrosyls. However, the contrasts in these chemistries are also noteworthy. 

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