Ligand effects upon the reactions of Ni(II) with sodium tetrahydroborate: Ni(I) complexes of bipyridyl and 1,10-phenanthroline

Abstract

. Can. J. Chem. 55, 4048 (1977). The reactions between NaBH, and Ni(I1) have been studied in the presence of a variety of ligands in an effort to determine (a) the conditions under which reduction occurs, (b) the extent of the reduction (e.g. to Ni(I), Ni(0) complexes, or to Ni metal or boride), and (c) whether intermediate Ni complexes can be isolated.With ligands having no n-bonding capabilities (NH3, ethylenediamine, edta, citrate), reduction depends upon the Ni:ligand ratio and, in the presence of an excess of the ligand, reduction of Ni(1I) is very slow. When vacant coordination sites exist on the metal through dissociation of, for example, Ni(NH,),'+, allowing for the interaction of the BH4 group with the metal, then rapid reduction to the metal (or boride) takes place.With the K-bonding N-donor ligands 1,lO-phenanthroline (phen) and 2,2'-bipyridyl (bipy) reduction of the stable ML,'+ complexes probably occurs via an outer-sphere electron transfer mechanism but, in these cases, new species of the type NiL2X (L = phen, bipy; X = BH4, PF6, BPh4), which formally contain Ni(I), have been isolated. Lorsque les ligands n'ont pas de capacitt de liaisons n (NH,, tthylknediamine, edta, citrate), la reduction depend du rapport Ni : ligand et, en prtsence d'un exces de ligand, la reduction de Ni(I1) est tres lente. Quand des sites de coordination vacants existent sur le metal par I'intermtdiaire d'une dissociation, par exemple de Ni(NH,),'+, permettant une interaction du groupe BH4 avec le metal, il y a alors une rtduction rapide conduisant au mttal (ou borure).Avec des ligands donneurs par l'azote et pouvant crter des liens K comme la phtnanthroline-1,10 (phen) et bipyridyl-2,2' (bipy) la reduction des complexes stables ML,,+ se produit probablement par l'intermkdiaire d'un mtcanisme de transfert Clectronique au niveau de la sphere exttrieure mais dans ces cas on peut isoler de nouvelles esfices du type NiL,X (L = phen, bipy; X = BH,, PF,, BPh4) qui contiennent d'une f a~o n formelle du Ni(1). [Traduit par le journal] IntroductionIt is known that the presence of certain ligands prevents the rapid reduction by NaBH, of metal salts to the metal or to the insoluble borides (1). Without doubt, reactions between NaBH, and transition metal complexes containing phosphines are best documented and, in the case of nickel, these proceed by two different routes.

Bis(ditertiaryphosphine) complexes of rhodium(I). Synthesis, spectroscopy, and activity for catalytic hydrogenation

“…ligand yielded a deep red precipitate but this decomposed even under Ar, and we have been unable to characterize the compound. Borohydride reduction of Rh(dpb),CI yielded a mixture of complexes that have not been separated; borohydride species are almost certainly present as judged by ir bands in the 2340-2390 cm-' region (22). Attempts to synthesize the HRh(dpb), complex via the routes used to synthesize the diop analogue from RhCI3,3H,O (10,11,21) were similarly unsuccessful.…”

Production of Ni(I) complexes from reactions between Ni(II) and NaBH4 in the presence of triphenylphosphine and some bidentate phosphines

“…We have previously noted (6) that neutral squareplanar Ni(l1) complexes (e.g. of N,N-diethyldithiocarbanlate and dimethylglyoxime) are unreactive towards NaBH, due, presumably, to the stability of the complexes and the reluctance of BH,-to interact with the vacant axial coordination sites on the metal.…”

“…1 to 3 and references therein) involves NaBH, reductions of Ni(I1) (4)(5)(6). By this method, compounds such as NiL,X (L = 1,lOphenanthroline, 2,2'-bipyridyl, X = BH,, PF,, or BPh, (6)) and [Ni(BH,)P,], (P = triphenylphosphine) (5) have been synthesized.…”

“…1 to 3 and references therein) involves NaBH, reductions of Ni(I1) (4)(5)(6). By this method, compounds such as NiL,X (L = 1,lOphenanthroline, 2,2'-bipyridyl, X = BH,, PF,, or BPh, (6)) and [Ni(BH,)P,], (P = triphenylphosphine) (5) have been synthesized. The latter was prepared by the reaction sequence and isolated as a pyrophoric solid which, from its diamagnetism and infrared spectrum, is thought to be a Ni-Ni bonded dimer with bridging BH, groups (5).…”

Reduction of Co(II) with NaBH4 in the presence of triphenylphosphine

“…The fact that Co(BH,)P,, do not react with (n = 2) or are decomposed by (n = 3) an excess of NaPF, or NaBPh, (unlike NiL,(BH,), L = 1,lOphenanthroline (13), and Ni(BH,)P, (14) where the BH, groups are exchanged for PF6-and BPh,-anions) implies a Co-BH, bond which is more covalent than ionic. Clearly the bonding between metal ions and BH, needs further attention.…”