Ligands n-bonded

Perhaps because of inadequate or non-existent back-bonding (p. 923), the only neutral, binary carbonyl so far reported is Ti(CO)g which has been produced by condensation of titanium metal vapour with CO in a matrix of inert gases at 10-15 K, and identified spectroscopically. By contrast, if MCI4 (M = Ti, Zr) in dimethoxy-ethane is reduced with potassium naphthalenide in the presence of a crown ether (to complex the K+) under an atmosphere of CO, [M(CO)g] salts are produced. These not only involve the metals in the exceptionally low formal oxidation state of —2 but are thermally stable up to 200 and 130°C respectively. However, the majority of their carbonyl compounds are stabilized by n-bonded ligands, usually cyclopentadienyl, as in [M(/j5-C5H5)2(CO)2] (Fig. 21.8). 

Zheng et al. treated potassium [l,2,4]diazaphospholides, obtained from the reaction of 3,5-disubstituted-[l,2,4]diazaphospholes with metallic potassium in THF, with [Cp RuCl]4 to afford [(T75-dp)RuCp ] type pseudoruthenocene complex (106) (Scheme 33). Sandwich structure with almost eclipsed orientation of two n-bonded ligands has been confirmed by X-ray crystal structure determination [110], Catalytic application of [(rf-dp)RuCp ] complexes in the Heck reaction has also been investigated [111]. 

The new chromium(iii) isocyanato-complex (Ph4As)3[Cr(NCO)e] has been prepared and its i.r. and electron spectra are consistent with N-bonded ligands. ° A mixture of K3[Cr(NCS)e] and m-xylidine (m-xyl) at 100 °C for 4—5 h gives (m-xyl)[Cr(NCS)4(m-xyl)2] as purple crystals. Salts with other cations have also been isolated, and p-xylidine forms the analogous derivatives. ... 

A number of selenocyanate compounds formulated as the adducts In(NCSe)3L have been reported5,92 with L = py n = 4), DMF (n - 3.5), Pr3PO (n = 3) and diantipyrylmethane (n — 2), but no structural details are available. The compounds In(NCSe)3L3 (L = bipy, phen) may well be salts of InL3+ and NCSe-, while the anionic complexes [In(NCSe)fi]3- are reported to involve an N-bonded ligand and six-coordinate indium.93,94... 

N-bonded ligand is formulated as the oxotriazeno group i.e. —N=N—NHPh.16... 

The structure of [NBu ]3[Re2(NCS)10]228 is interesting because it contains both 1,1-ji-N-bonded and terminal N-bonded ligands. Surprisingly this difference in bonding is not reflected by the N—C and C—S distances. In the other Re260-265 and Tc261,266 thiocyanate complexes the terminally bonded form has been found. 

The cyanate complexes of the Group VIII metals are less common. A terminal N-bonded ligand is present in Ni(NCO)2(phen)2263a and a l,3-/i-bonded NCO in dimeric [BPh4][Ni2(tren)2(NCO)2] (cf. 100).230... 

In addition to many structure determinations by X-ray diffraction, nmr studies using 14N and 15N have allowed the comparison of NR with other N-bonded ligands like NO, NNR, etc.140... 

Based in part on the article Organic Synthesis using Transition Metal Complexes Containing n -Bonded Ligands by Martin F. SemmeUiack which appeared in the Encyclopedia of Inorganic Chemistry, First Edition. 

The alkyl derivatives of Au were discovered by W. J. Pope and C. S. Gibson in 1907 they include some of the most familiar and stable organo compounds of the group, and are notable for not requiring the stabilizing presence of n-bonding ligands. They are of three types ... 

However, over the last 60 years a new type of chemistry has emerged. Although the first examples, tertiary arsine complexes, were initially prepared as an extension of classical rhodium (III) chemistry, the newer complexes containing n-bonding ligands have been a consequence of the intense interest in the catalytic properties of rhodium(I) complexes. Examples of these ligands also include tertiary phosphines and stibines, although it is debatable to what extent they act as 7T-acids when coordinated to rhodium(III). 

Presumably dinuclear with bidentate bridging and terminal N-bonded ligands 1862... 

N-Donor Ligands. The isocyanato-complexes of Zr and Hf, (Et hOi-[M(NCO)g], have been prepared by the reaction of MCI4 with Et NNCO (1 2), followed by the addition of AgNCO (4 moles). The i.r. and Raman spectra of these complexes are consistent with N-bonded ligands. The analogous N-bonded selenocyanato-derivatives, K2[M(NCSe)g], have been prepared by the extraction of MCI4 into a MeCN solution of KNCSe. [M(bipy)2(NCS)4] and [M(phen)3(NCS)4] (M = Zr or HO have been prepared in THF-MeCN solutions and their i.r. and X-ray diffraction spectra reported. ... 

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