No abstract

A series of cis and trans Fe(II) complexes containing the diphosphine ligand PNP (where PNP is bis((diethylphosphino)methyl)methylamine) have been prepared and isolated. These include cis-[Fe (PNP) 7), trans-HFe(PNP)(dmpm)Cl (8), and trans-[HFe(PNP)(dmpm)(CH 3 CN)]BPh 4 (9) (where dmpm is bis(dimethylphosphino)methane). In addition, the cations trans-[HFe-(PNP)(dmpm)(CO)] + (10) and trans-[(H 2 )Fe(PNP)(dmpm)(H)] + (11) have been observed in solution. These complexes all possess a pendant base that bridges the two phosphorus atoms of the PNP ligand. A cis geometry is observed for those complexes containing two PNP ligands, whereas a trans geometry is observed for the complexes containing one PNP ligand and one dmpm ligand. The molecular structures of cis-[Fe(PNP) 2 (CH 3 CN)(CO)](BPh 4 ) 2 and trans-[HFe(PNP)(dmpm)(CH 3 CN)]BPh 4 have been confirmed by X-ray diffraction studies. Protonation of 5, 7, and 10 occurs at the nitrogen atom of the PNP ligand, and pK a values are reported for the corresponding protonated complexes. The formation of the dihydrogen complex [trans-[(H 2 )Fe(PNP)(dmpm)(H)] + and the protonated PNHP complex trans-[HFe-(PNHP)(dmpm)(CO)] 2+ demonstrate that intramolecular heterolytic cleavage of the dihydrogen ligand can be controlled by varying the nature of the ligand trans to the incipient dihydrogen ligand.

A series of new iron(II)-hydride complexes that contain diphosphine ligands with pendant amine bases of the formula cis-[HFeL(PNP) 2 ] + , where PNP ) Et 2 PCH 2 NMeCH 2 PEt 2 and L ) CH 3 CN (3), CO (4), P(OEt) 3 (5), have been synthesized and characterized. Protonations of the pendant bases in the PNP complexes have been characterized, and for selected complexes, pK a values have been determined. The acidity of the PNHP ligand depends significantly on the electronic properties of the Fe center to which it is bound, ranging from <7.0 to 12.7, depending on the nature of the coligands present. Unlike the previously studied hydride complexes [HNi(PNP) 2 ] + and trans-[HFe(CH 3 CN)(PNP)(dmpm)] + (where dmpm is bis(dimethylphosphino)methane), the new hydride complexes reported here do not show rapid intramolecular exchange between the protonated base of the diphosphine and the hydride ligand. This is attributed to steric interactions between ethyl substituents on the PNP ligands.

A series of new iron(II) complexes that contain cyclic diphosphine ligands with pendant amine bases, P 2 R N 2 R′ , have been synthesized and characterized (where P 2 R N 2 R′ are substituted 1,5-diaza-3,7diphosphacyclooctanes). These compounds include [Fe(P 2 Ph N 2 Ph )(CH 3 CN) 7), and cis-Fe(P 2 Ph N 2 Ph ) 2 (Cl) 2 (8). The molecular structures of 5, 6b, and 7 have been confirmed by X-ray diffraction studies. For all complexes the cyclic diphosphine ligands contain one six-membered ring in a chair conformation and one six-membered ring in a boat conformation. For complex 7, the two rings that are in boat conformations result in N-H distances between the pendant amine nitrogens and the hydride ligand of 2.6 to 2.7 Å. Protonation of the pendant bases in complex 7 has been found to form several products. A structural assignment for a dominant protonated isomer has been assigned on the basis of 1 H, 31 P, and 15 N NMR spectroscopic techniques.

The Group I salts of 12-tungstophosphoric acid were studied in their limiting hydration state with use of bothH and 31P solid-state nuclear magnetic resonance (NMR). The bulk proton structures of the Li, Na, and Rb salts consist of both lone protons and water molecule protons. The K and Cs salts contain similar proton structures that reside in surface sites. Nonspinning 1H NMR results indicate that all protons in the limiting hydration state in each of the Group I salts are highly mobile at room temperature. 1H spin−lattice relaxation times obtained as a function of temperature indicate that the dominant mechanism responsible for proton relaxation in the Li, Na, and Rb salts is restricted rotation of water molecules while the K and Cs salts have proton spin−lattice relaxation that is dominated by translation of protons through surface sites of the material. Two stable Rb salt phases are crystallized when a stoichiometric amount of RbCl is added to aqueous 12-tungstophosphoric acid at room temperature.