Cyclopentadienyl carbonyl complexes

There are presently few studies on the complexes r-C5H5M(CO)4 where M = V, Nb or Ta. The crystal structures of the vanadium [150a] and niobium [150i ] compounds show them to have the structures given on pp. 92, 134. Some reactions of the vanadium compound are  

The cation [(7r-CsH5)2V(CO)2] , which is isoelectronic with (jr-C5H5)2Ti(CO)2, is prepared in the reaction between vanadocene, V(CO)6 and carbon monoxide at 15° [132]. 

Some chemistry of w-cyclopentadienyl molybdenum complexes 

Many derivatives of r-cyclopentadienylmolybdenum carbonyls with sulphur ligands are known, e.g. tt-C5H5Mo(CO)2S2CSR [158cz], and the anion [n -C5H5Mo(CO)2S2C2(CN)2]- [158i]. 

Prolonged refluxing of [7r-C5H3Fe(CO)2]2 in benzene gives the tetrameric complex 4.10a, where X = CO [162a]. 

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Mono( 17-cyclopentadienyl) carbonyl complexes of Ti, Zr, and Hf have been noted only in the patent literature. A U.S patent issued to Ethyl Corporation in 1962 described the use of such complexes as anti-knock agents and lubricant additives. Two examples of complexes purported to have been made are shown below (115). 

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... 

Cyclopentadienyl carbonyl complexes, with niobium, 5, 64 Cyclopentadienyl chromium bis(Ti-allyl) complexes, with chromium, 5, 305-306 Cyclopentadienyl chromium carbonyls... 

C-H bond dissociation energies, 1, 298 C-N triple bond additions, 10, 427 C02, ketene, ketenimine complexes, 5, 84 CO and CNR reductive coupling, 5, 66 cyclopentadienyl alkyl and aryls, 5, 66 cyclopentadienyl carbonyl complexes, 5, 64 cyclopentadienyl hydrides, 5, 69 cyclopentadienyl isocyanide complexes, 5, 65 rf-acyl and rj2-iminoacyl complexes, 5, 82 fj3-complexes, 5, 87... 

In this case (compare with Ref. 268), the Te — Te bond remains. This bond is not destroyed also under interaction of diphenylditellurides with cyclopentadienyl-carbonyl complexes of manganese (3.99a) [272] and iron (3.99b) [273] ... 

The transformation of P4 in the coordination sphere of 15 VE fragments has been studied by allowing group-6 carbonyls, [M(CO)6] (M=Cr, Mo, W), and nickel cyclopentadienyl carbonyl complexes to react using Scheer s one-pot/three-components practice under thermal or photochemical conditions. Remarkably, the combination of P4, [Cr(CO)6], and the nickel dimer [ Cp Ni (CO) 2] under UV irradiation yields complexes incorporating Pj, P2, and P3 lig-... 

Reactivity patterns for cyclopentadienyl-carbonyl complexes are similar to those found for arene complexes, i.e., the dominant photoreaction is CO loss. In h -CjH5M(CO)3X (X = Cl, Br, 1) complexes, the quantum yields are high and the process is stereospecif-ic only cis substitution is observed ... 

Although cyclopentadienyl-carbonyl complexes are photosensitive, nearly all decay by loss of CO, with the cyclopentadienyl ligand not being involved. However, this... 

The atomic number ofMn = 25 25 -1-5 -l-(3 X2) = 36 electrons the mle is satisfied. This mixed cyclopentadienyl carbonyl complex is of importance as an antiknock compotmd in gasoline. 

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