Mononuclear seven-coordinate

The binuclear tungsten(II) and molybdenum(II) compounds react with phosphorous and nitrogen atom donor ligands and after chloride bridge splitting give mononuclear seven-coordinate compounds. 

In the reaction of a bimetallic tungsten-tin compound with acetonitrile we isolated and characterised structurally a mononuclear seven-coordinate compound with two mutually cis nitrile ligands and a trichlorostannyl moiety coordinated to tungsten through a direct tungsten-tin bond and a chloride bridge (Eq. 4) [39]. 

The reactivity of molybdenum carbonyls in reaction with Lewis acids is comparable to the reactivity of tungsten carbonyls. The treatment of a nitrile carbonyl compound with an equimolar amount of tetrachlorotin in dichloromethane gives the oxidative-addition product, a mononuclear seven-coordinate compound [MoCl(SnCl3)(CO)3(NCMe)2], in good yield [36, 40]. The same compound was isolated from the reaction of a binuclear compound and acetonitrile. The crystal structure of the reaction product is similar to that... 

The binuclear compounds as well as the mononuclear seven-coordinate bis(nitrile) compounds are catalysts for the polymerisation of terminal alkynes such as phenylacetylene (PA) or ferf-butylacetylene (f-BA) and for the ROMP of norbornene (NBE) and norbornadiene (NBD) [20, 38-42]. The first step in all catalytic reactions is the coordination of the organic substrate to metal and the formation of a complex. Sometimes it was possible to isolate the products in crystalline form but frequently such adducts were observed only in situ by NMR investigations. 

Reactions of Mo2l (CO)g with ligands lead to mononuclear seven-coordinate [M0I2(CO)3L2]... 

Divalent molybdenum compounds occur in mononuclear, dinuclear, and hexanuclear forms. Selected examples are shown in Figure 6. The mononuclear compounds are mostiy in the realm of organometaUic chemistry (30—32). Seven-coordinate complexes are common and include MoX2(CO)2(PR3)2, where X = Cl, Br, and I, and R = alkyl MoCl2(P(CH3)3)4, heptakis(isonitrile) complexes of the form Mo(CNR) 2 (Fig. 6d), and their chloro-substituted derivatives, eg, Mo(CNR)3CR. The latter undergo reductive coupling to form C—C bonds in the molybdenum coordination sphere (33). 

A mononuclear diastereopure high-spin Fe alkylperoxo complex with a pen-tadentate N,N,N,0,0-ligand 33 (Scheme 17) was reported by Klein Gebbink and coworkers [109, 110]. The complex is characterized by unusual seven-coordinate geometry. However, in the oxidation of ethylbenzene the iron complex with 33 and TBHP yielded with large excess of substrate only low TON s (4) and low ee (6.5%) of 1-phenylethanol. 

The unusual complex p-F-[MoO(02)(pydca)]j (see 5) is formed as the NEt4 salt upon treatment of Mo(02)(pydca)(OH2) with F 418 in the presence of NEt4. The complex, shown in Figure 21, is a centrosymmetric dinuclear ion with each Mo atom possessing pentagonal bipyramidal seven-coordination.307 The linear OtMoVIFMoVIOt unit is to date unique to this complex. The Mo—O, distance is 1.659(3) A and the Mo—F trans to it has the very long distance of 2.135(1) A. The O—O distance of 1.43 A is similar to that found in mononuclear peroxo compounds of Mo . 

A simple example of an AxByCz donor hgand of higher denticity is (126), which carries a NS2P2 donor set, and binds as a pentadentate in a seven-coordinate bis(triflato)cadmium(ll) complex However, mononuclear Cu, Ag, and Au complexes are four-coordinate with the ligand behaving as a P2S2 donor, indicative of the... 

Some V complexes involving the ONO donor ligand pyridme-2,6-dicarboxylic acid, (DPA), include the seven-coordinated mononuclear complex, [V(DPA)(PA)(H20)2]... 

The introduction of bis(p-chlorophenyl) and bis(methylthio) substituents in the 4 - and 4"-positions of quinquepyridine (35) (that is, on the backbone of the second and fourth pyridyl rings in the string) was reported to have little effect on the coordination behaviour of these ligands relative to that of the unsubstituted analogue (see earlier). Namely, with nickel(II) and copper(I) and/or copper(II), doublehelical 2 2 complexes were obtained, while cobalt(II) forms both a 1 1 and a 2 2 complex in the solid state (although, in solution only a mononuclear seven-co-ordinate complex occurs - with the solid state, double-helical structure interconverting to this form upon dissolution). 

Mononuclear Viv complexes of substituted hydroxamates have been characterized with 1,10-phenanthroline or 2,2 -bipyridine as supporting ligands. A seven-coordinate vanadium atom was proposed to exist in these complexes, although a six-coordinate complex may be more likely.652 A range of hydroxamate-containing complexes have been prepared and were subsequently found to facilitate transport of Viv into cells.653... 

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