Chelating ligands have proven instrumental in the development of new catalysts; furthermore trans-chelating "pincer" ligands have garnered considerable attention over the years. 1À13 The most extensively investigated pincer complexes feature ligands based on a meta-substituted arene skeleton (PCP). Variations of the PCP-pincer framework have been shown to alter the electronic and steric properties of the corresponding metal complexes, resulting in unique reactivity. 14,15 Aminophosphine chelating ligands of the form (linker)-(NR 0 PR 2 ) 2 have also garnered attention, as such ligands are readily prepared from diamines and chlorophosphines. 5,16 While linked diaminophosphine ligands such as (CH 2 N(R 0 )PR 2 ) 2 (R 0 = H, alkyl; R = alkyl, aryl) have been reported by Wollins, 17 Gusev, 9 Vogt, 16 and others, 18À21 investigations of PCP aminophosphine-based pincer ligand complexes have received less attention. 10 We were drawn to these systems, as such ligands offer adjacent P and N donors, suggesting the possibility of unique binding modes and thus subsequent reactivity. In this regard, the only report in which the N atom of an aminophosphine has been shown to participate in binding to a metal was recently reported by Palacios et al. In this case a bis-aminophosphine ligand was shown to bind to Ru via both P atoms as well as one of the amino NH groups, affording the Ru cation [Cp*Ru(k 3 P,N,P-(iPr 2 PNH) 2 C 6 H 10 ] + . 21 In this paper, we describe the synthesis and characterization of Ni and Pd complexes of bis-aminophosphine chelating ligands. Interestingly, these ligands are shown to readily adopt two tridentate binding modes. Participation of the secondary N adjacent to P affords k 3 P,N,P ligands that incorporate three-membered NPM metallacycles. Alternatively, metalation of the alkyl chain in the ligand backbone affords k 3 P,C,P pincer complexes.

We have examined the reaction of hydantoin (¼ imidazolidine-2,4-dione) with (formylphenyl)boronic acids, where the addition of a boronic acid group is hoped to increase bioactivities. Addition of (2-formylphenyl)boronic acid to hydantoin gave an unexpected azaborine compound, which presumably arises by initial formation of the (phenylmethylidene)hydantoin, with subsequent loss of H 2 O to give the cyclized product. Reactions of (3-formylphenyl)-and (4-formylphenyl)boronic acids with hydantoin gave the corresponding [(Z)-phenylmethylidene]hydantoins in good-to-excellent yields. Attempts to use (3-formylthiophen-2-yl)boronic acid gave a product where the boronic acid group has been cleaved.