Cyclopentadienyl carbonyl/nitrosyl compounds

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... 

As indicated above, the antiknock effect is shown by many compounds. Outstanding among these are the organometallic compounds of many metals. Effective derivatives of many metals include alkyl compounds, aryls, carbonyls, nitrosyls, phosphines, cyclopentadienyls, and many mixed compounds. The aromatic amines are also good antiknock agents, but far less effective than the organometallic compounds. The reason why commercialization efforts were concentrated on tetraethyllead early in the history of antiknock investigations is evident from Table 1, which is a composite of early data 6 8,216). 

The chemistry of the dicarbonyl(7 -cyclopentadienyl)nitrosyl and the chloro-(i7 -cyclopentadienyl)dinitrosyl complexes of chromium, molybdenum, and tungsten [i.e., fT -CsHs)M(CO)j(NO)] and [(i7 -CsHs)M(NO)2Cl] has not been studied extensively, partly because of the various difficulties associated with their preparation. The procedures described below are of general applicability to all three metals and lead to the desired compounds in high yields. The carbonyl nitrosyl complexes are the synthetic precursors of the chloro nitrosyl complexes and so their preparation is described first. 

Before reviewing the other physical data on organometallic nitrosyls we now summarize the purely chemical information on the compounds. For convenience the material has been divided into three main categories (a) nitrosyl carbonyls and nitrosyl isocyanides (b) nitrosyl cyano species and (c) cyclopentadienyl and miscellaneous organometallic nitrosyls. 

Ruthenium(II), d, is known as the binary bromide and as [RuCU] ". The richer complex chemistry involves stable compounds with cyanide, amines, halides, water, nitrosyl, carbonyl, hydride, phosphine, arsine, stibine, arene, and cyclopentadienyl ligands. [RuCl2(PPh3)2] is used as a catalyst. Ruthenium(II) is a good itt-donor and... 

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]. 

The metals bonded to two cyclopentadienyls (Cp) in a pentahapto mode form the metallocenes (see Chap. 11 also describing the Cp-M orbitals). In many other families of compounds, the metal is bonded to only one Cp or derivative. Common examples of this category include ternary families containing, besides the Cp-type ligand, carbonyls, phosphines, nitrosyls, hydrides, 0x0, imido, methyls, etc. - ... 

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