With dppe bidentate ligand

It is noteworthy that a clear enhancement of selectivity for the linear hydro-formylation product is observed only with cdpp (Table 5.2-1, entry e). With all other ligands, the n/iso ratios are in the 2 to 4 range. While this is in accordance with known results in the case of PPI13 (entry a) and dppe (entry c) (in comparison to monophasic hydroformylation [69]) and also with reported results in the case of Natppts (entry b in comparison to the biphasic hydroformylation of 1-pentene in [BMIM][PF(3] [46]), it is more remarkable for the bidentate metallocene ligand dppf... 

The pyridine ligand in the products shown in Scheme 126 is labile and can be readily replaced by bidentate ligands such as 1,10-phenanthroline (phen) or l,2-bis(diphenylphosphino)ethane (dppe). Scheme 127 illustrates the reaction with phen. ... 

The adducts involving bidentate ligands are all of type [M2C16(LL)2]. The structures of those with bidentate phosphines (M = Nb, LL = dppe 602 M = Ta, LL = dmpe595) are related to that of (31), but with the chelate rings spanning two equatorial positions. The metal-metal distances are consistent with either a double or a single bond (Nb—Nb 2.712(2) A Ta—Ta 2.710(1) A). 

The three-coordinate intermediate in Equation 19 would then allow for greater mobility of the groups from which reductive elimination could proceed.(19) Rearrangement followed by a very rapid reductive elimination the cis isomer is also a possibility. However, our unsuccessful attempts to synthesize cis-aryl-methyl-nickel(ll) complexes still leave open the question of reductive elimination from such stereoisomers. The results we obtained in studies with the bidentate diphosphine ligand (dppe), though qualitatively in this direction, unfortunately lack definitiveness as yet. 

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