Cyclopentadienyl nitrosyl complexes

An interesting bridging nitro l complex has been obtained by the reduction reaction. 

In the complex, 4.15, the terminal nitrosyl frequencies occur at 1672 cm i whilst the bridging nitrosyls show a stretch at 1505 cm-i [197,198]. Related complexes are [jr-CsHsCrNOX]2 where the bridging ligand X may be for 

Other complexes in this class include the polymeric [jr-C5HjMn(NO)2] , [1986]. 

Brief notes on Innuclear n-cyclopentadienyl complexes cmitaining 

7i-cyclopentadienyl metal complexes [204, 205, 206], Of great interest is the complex 4.18, which X-ray analysis shows to be symmetrical, and it is proposed that the hydrogen bridges the two molybdenum atoms symmetrically [207]. 

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A. DICARBONYL(t -CYCLOPENTADIENYL)NITROSYL complexes of CHROMIUM, MOLYBDENUM, AND TUNGSTEN... 

Nitric oxide, like the 7r-allyl group, can act as a 3-electron ligand a number of stable a -cyclopentadienyl nitrosyl complexes are known. The preparations of some of these complexes are shown in Figures 30 and 32. The series tt-CsHsMNO, where M = Ni [28], Pd [194], and Pt [195], is well characterized and the microwave spectrum of the nickel complex shows the synametric structure given in Figure 28, p. 112 [196]. In this molecule, the short Ni-N distance (1-676 0-02 A) indicates considerable multiple bonding. The dinitrosyl n -C5H r(NO)2CI similarly has a short Cr-N bond (1-72 A) [196a]. 

Substituted derivatives of nickelocene, where one ring has been replaced, include the complex cyclopentadienyl nitrosyl nickel [12071 -73-7], (7T-C3H3)NiNO, a red Hquid, mp -41°C. A review of nitrosyl complexes with nickel is available (89). The dimer complex... 

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... 

Some cyclopentadienyl-/x-mercapto-, -alkoxo-, and /a-dialkylamido-chromium nitrosyl complexes (VI)-(X) have been studied by Preston and Reed 167). 

An interesting synthesis of the cyclopentadienyl bisphosphine ruthenium nitrosyl complex 9 involves the thermal displacement of both phenyl groups from (i75-C5H5)Ru(NC))PIi2 (8) with a chelating diphosphine [Eq. (6)] (72). Infrared data indicate that the nitrosyl ligand is linear (3 e ... 

Cyclopentadienyl) (or related hgand). Treatment of (ry -allyl)dicarbonylnitrosyliron complexes (see Nitrosyl Complexes) with phosphite or phosphine gives five-coordinate ()] -allyl) complexes (22) of limited stability. The reaction of Fe(t-BuNC)5 with both aUyl bromide and chloride gives a product formulated as (23). Compounds of the general stracture (24) were prepared by reaction of [(CO)4Fe(SiR3)] and HFe(CO)4(SiR3) with allyl bromide and isoprene, respectively. ... 

The cubane-like cluster [ Fe(/X3-S)(NO) 4] (68) is not formally an organometallic compound, but the structural changes observed when it is reduced, and the MO description of its bonding, are relevant to the cyclopentadienyl complexes described above. The nitrosyl complex contains 60 valence electrons, 8 less than [ Fe()U3-S)Cp 4], and is reduced in two consecutive one-electron steps to an isolable monoanion [68] , and to a dianion [68] . 

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. 

The preparations of all three (tj -CsH5)M(CO)2(NO) complexes from their corresponding [(tj -CsHs)M(CO)3] anions are similar. The experimental procedure, using the tungsten complex (dicarbonyl(i7 -cyclopentadienyl)nitrosyl-tungsten) as a typical example, is given below. 

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