B-Donor ligands

Group III Donors. B-donor ligands. In an extension of recent studies on Ptn-borallyl complexes, a unique series of complexes of the 71-83117 ligand have been prepared with Ni, Pd, and Pt  

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There is also clear evidence of a change from predominantly class-a to class-b metal charactristics (p. 909) in passing down this group. Whereas cobalt(III) forms few complexes with the heavier donor atoms of Groups 15 and 16, rhodium(III), and more especially iridium (III), coordinate readily with P-, As- and S-donor ligands. Compounds with Se- and even Te- are also known. Thus infrared. X-ray and nmr studies show that, in complexes such as [Co(NH3)4(NCS)2]" ", the NCS acts as an A -donor ligand, whereas in [M(SCN)6] (M = Rh, Ir) it is an 5-donor. Likewise in the hexahalogeno complex anions, [MX ] ", cobalt forms only that with fluoride, whereas rhodium forms them with all the halides except iodide, and iridium forms them with all except fluoride. 

Also in the divalent state, Pd and Pt show the class-b characteristic of preferring CN and ligands with nitrogen or heavy donor atoms rather than oxygen or fluorine. Platinum(IV) by contrast is more nearly class-a in character and is frequently reduced to Pt by P- and Aj-donor ligands. The organometallic chemistry of these metals is rich and varied and that involving unsaturated hydrocarbons is the most familiar of its type. 

Mixed 6),Af-donor ligands such as Schiff bases are of interest in that they provide examples not only of square-planar coordination but also, in the solid state, examples of square-pyramidal coordination by dimerization (Fig. 28.6(b)). A similar situation occurs in the bis-dimethylglyoximato complex, which dimerizes by sharing oxygen atoms, though the 4 coplanar donor atoms are all nitrogen atoms. Copper(II) carboxylates are easily obtained by crystallization from aqueous solution or, in the case of the higher carboxylates, by precipitation with the appropriate acid from ethanolic solutions... 

Koppikar DK, Sivapullaiah PV, Ramakrishnan L, Soundararajan S (1978) Complexes of the Lanthanides with Neutral Oxygen Donor Ligands. 34 135-213 Keren B, see Valach F (1984) 55 101-151... 

Few quantitative data are available on the relative nucleophilicities of L toward various alkyl carbonyls. The rates of the reaction of CpMo(CO)3Me with L in toluene (Table II) decrease as a function of the latter reactant P( -Bu)3 > P( -OBu)j > PPhj > P(OPh)j, but the spread is relatively small (<8). The above order is that customarily observed for 8 2 reactions of low-valent transition metal complexes (J, 214). Interestingly, neither CpMo(CO)3Me nor CpFe(CO)2Me reacts with 1 or N, S, and As donor ligands 28, 79). This is in direct contrast to the insertion reactions of MeMn(CO)5 which manifest much less selectivity toward various L (see Section VI,B,C,D for details). 

Subtle electronic effects were also observed for the Sasol ligands, as in the series X = CN, Ph, OBz, Me a decrease in the rate of reaction was found while the linearity followed the reverse trend the better donor gives the highest linear to branched ratio (4.9, very similar to the best Shell catalyst 170 °C, 85 bar). As the authors remarked, this is not an intrinsic ligand effect on the reaction it is a measure of the amount of phosphine-free catalyst 5 that is present in the equilibrium. Thus the weaker donor ligands give more 5 and thus a higher rate and a lower l b ratio. This was supported by IR and NMR measurements. 

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