N-Bidentates

Complexes with chiral heterocycles possessing P-containing substituents as P-mono- andP,N-bidentate ligands and their use in homogeneous asymmetric catalysis 98KK883. 

Chiral P-heterocycles as P-mono- and P,N-bidentate ligands in the synthesis of coordination compounds and homogeneous asymmetric catalysis 98KK883. 

A review8 with more than 186 references discusses the synthesis of Rh and Pd complexes with optically active P,N-bidentate ligands and their applications in homogeneous asymmetric catalysis. The effect of the nature of the P,N-bidentate compounds on the structure of the metal complexes and on enantioselectivity in catalysis was examined. Allylic substitution, cross-coup-ling, hydroboration and hydrosilylation catalyzed by Rh or Pd complexes with optically active P,N-bidentate ligands are considered. 

Bidentate ligand systems are also known with selenium and nitrogen donors. For example, Se/N bidentate phosphinochalcogenoic ligand and zinc amides react to form a distorted tetrahedral complex with two di-t-butylphosphinoselenoic isopropylamidate ligands.590... 

Phosphinodihydroxazole (PHOX) compounds, L2-4, act as P/N bidentate ligands showing excellent enantioselectivity in Ir-catalyzed hydrogenation of simple a,a-disubstituted and trisubstituted olefins (Figure 1.12). " The use of tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (BArp) as a counter anion achieves high catalytic efficiency due to avoidance of an inert Ir trimer... 

A,TV-Dimethyl-A -phenylthiourea has been shown to coordinate to Rh111 as an N—S bidentate involving four-membered chelate ring formation.154 N-Substituted thioamides also may bond in this manner.155 156 l-Amidino-2-thioureas (44) may behave either as N—S or as N—N bidentates, with this donor choice being dependent mainly on pH and the nature of the metal ion.157 As N—S donors they are known to stabilize lower oxidation states.158 As part of a study on Mo—S-containing complexes as models for redox-active molybdoenzymes, Dilworth et al. have shown that some p-(substituted)phenylhydrazines may coordinate as N—S bidentates in three different ways to one metal atom.159 The three diazenido, diazene and hydrazonido forms vary in their degree of deprotonation and therefore their anionic nature. 

MIXED DONOR BIDENTATES CONTAINING SELENIUM 20.4.5.1 Se—N Bidentates... 

Some other Lewis base adducts of lead(II) compounds are the 2 1 adducts of the N,N bidentate aromatic base 1,10-phenanthroline (phen) with lead(II) nitrate and perchlorate126. 

Only two such complexes will concern us here. One of them, the doubly bonded dirhenium(II) complex Re2Cl6(Ph2Ppy)2 which contains the mixed P—N bidentate 2-(diphenylphosphino)py-ridine ligand, has been described in Section 43.5.2.4. The other complex is Re2(hp)4Cl2 (Hhp = 2-hydroxypyridine), which is prepared by the reaction of (BuJN)2Re2Cl8 with the molten ligand and has a structure very similar to that of Re2(02CR)4X2 (41), but with an even shorter Re—Re bond distance (2.206(2)A versus 2.24A).175... 

Albinati et al. have studied the three-dimensional structure of PtCl2L and PdCl2L metal complexes [P,N bidentate L=(p-CH3CgH4)2PCH2CH(Pr )NHCH2-... 

A. Albinati, F. Lianza, H. Berger, P. S. Pregosin, H. Riiegger, and R. Kunz, Inorg. Chem. 32, 478 (1993). Preparative and Structural Chemistry of Chiral P,N-Bidentate Complexes of Palladium(II) and Platinum(II). 

New N,N bidentate SB ligands derived from 3-acetyl-pyridine and hydrazine have been prepared and crystallographically characterized.37 The specific geometry of these ligands gives coordination polymers with novel network patterns. 

The IR and Raman spectra of SnX4(DMPP) and R2SnX2(DMPP), where X = Cl, Br or I R = Me, Et, Bu or Ph DMPP = 3,5-dimethyl-1-(2 -pyridyl)pyrazole, were all consistent with the presence of an N,N bidentate ligand.206... 

Scheme 4.25 Cinchona alkaloids derived P,N-bidentate ligands 40a-d for the asymmetric allylic alkylation reaction.

---