Six complexes of the type trans-[Fe(NCMe)2(P-N-N-P)]X2 (X = BF4(-), B{Ar(f)}4(-)) (Ar(f) = 3,5-(CF3)2C6H3) containing diiminodiphosphine ligands and the complexes trans-[Fe(NCMe)2(P-NH-NH-P)][BF4]2 with a diaminodiphosphine ligand were obtained by the reaction of Fe(II) salts with achiral and chiral P-N-N-P or P-NH-NH-P ligands, respectively, in acetonitrile at ambient temperature. The P-N-N-P ligands are derived from reaction of ortho-diphenylphosphinobenzaldehyde with the diamines 1,2-ethylenediamine, 1,3-propylenediamine, (S,S)-1,2-disopropyl-1,2-diaminoethane, and (R,R)-1,2-diphenyl-1,2-diaminoethane. Some complexes could also be obtained for the first time in a one-pot template synthesis under mild reaction conditions. Single crystal X-ray diffraction studies of the complexes revealed a trans distorted octahedral structure around the iron. The iPr or Ph substituents on the diamine were found to be axial in the five-membered Fe-N-CHR-CHR-N- ring of the chiral P-N-N-P ligands. A steric clash between the imine hydrogen and the substituent probably determines this stereochemistry. The diaminodiphosphine complex has longer Fe-N and Fe-P bonds than the analogous diiminodiphosphine complex. The new iron compounds were used as precatalysts for the hydrogenation of acetophenone. The complexes without axial substituents on the diamine had moderate catalytic activity while that with axial Ph substituents had low activity but fair (61%) enantioselectivity for the asymmetric hydrogenation of acetophenone. The fact that the diaminodiphosphine complex has a slightly higher activity than the corresponding diiminodiphosphine complex suggests that hydrogenation of the imine groups in the P-N-N-P ligand may be important for catalyst activation. Evidence is provided, including the first density-functional theory calculations on iron-catalyzed outer-sphere ketone hydrogenation, that the mechanism is similar to that of ruthenium analogues.

The reaction of RuHCl(PPh3)3 with the tetradentate ligand [PPh2((ortho-C6H4)CH2NHCH2 - )]2 {ethP2(NH)2} in THF produces the new complex trans-RuHCl{ethP2(NH)2} (1) as a mixture of two isomers. The complex RuHCl{ethP2(NH)2} (1) when activated with KOtBu/KH is a very active catalyst for the hydrogenation of benzonitrile to benzylamine in toluene, more active than the known catalyst Ru(H2)2H2(PCy3)2 (2). A mixture of 1 and 2 and base also results in efficient conversion of benzonitrile to benzylamine. The complex RuHCl{tmeP2(NH)2} (3) where tmeP2(NH)2 is [PPh2((ortho-C6H4)CH2NHCMe2 - )]2 is a less active catalyst for this reaction. These catalyst systems are air sensitive and extremely moisture sensitive. Experimental and theoretical (DFT) evidence is presented for a new mechanism for nitrile hydrogenation:  the successive hydrogenation of the CN triple bond and then the CN double bond of the intermediate imine by H+/H- transfer from a trans dihydride active catalyst. The amido complex RuH{tmeP2N(NH)} (4) has similar activity to 3/base for the base-free hydrogenation of benzonitrile and is moderately active for the catalytic hydration of benzonitrile. The new complex RuH(BH4){ethP2(NH)2} (7) was prepared by reacting 1 with NaBH4 but is found to be a poor catalyst for nitrile hydration.

The trans-dihydride complex trans-RuH(2)(NH(2)CMe(2)CMe(2)NH(2))((R)-binap) (1) is an active catalyst for the homogeneous hydrogenation of ketones in benzene under pressure of H(2) gas. The mechanism of the catalysis is proposed to occur through a rapid transfer of a hydride from the ruthenium and a proton from the amine on 1 to the carbonyl of the ketone to give the product alcohol and a hydrido-amido intermediate RuH(NHCMe(2)CMe(2)NH(2))((R)-binap) (2). The dihydride is then regenerated by the turnover-limiting heterolytic splitting of dihydrogen by complex 2. In this work the kinetic isotope effect (KIE) is measured to be 2.0 (+/-0.1) for the reduction of acetophenone to 1-phenylethanol catalyzed by 1 using 8.0 atm of H(2) versus D(2) gas. DFT calculations predict a KIE of 2.1 for the described mechanism using the simplified catalyst RuH(NHCH(2)CH(2)NH(2))(PH(3))(2) with H(2) or the catalyst RuD(NDCH(2)CH(2)ND(2))(PH(3))(2) with D(2). This supports the observation that deuterium scrambles into the catalyst when a pressure of D(2) is used. We discuss the significance of these results relative to the KIE of 2 that was reported by Sandoval et al. (J. Am. Chem. Soc. 2003 125, 13490) for the hydrogenation/deuteriation of acetophenone catalyzed by trans-RuH(eta(1)-BH(4))((S)-tolbinap)((S,S)-dpen) in basic isopropanol/isopropanol-d(8).

The reaction of the iron complex trans-[Fe(CO)(MeCN)(PPh 2 C 6 H 4 CHNCH 2 −) 2 -κ 4 P,N,N,P]-(BF 4 ) 2 (1) with KOiPr in benzene produced the unusual complex [Fe(CO)(PPh 2 C 6 H 4 CHNCH 2 CH 2 NHCHC 6 H 4 PPh 2 )κ 5 P,N,C,N,P][BF 4 ] (2), which has been characterized by spectroscopy and by single-crystal X-ray diffraction. The C−N bond length in this complex indicates that it is best viewed as an iron(II) ligand-folded ferraaziridine-κ 2 C,N complex instead of an iron(0) η 2 -iminium complex. Density functional theory (DFT) calculations have been employed on simplified structural models to support a mechanism of formation of this complex via the transfer of a hydride from the alkoxide complex trans-[Fe(CO)(OCHMe 2 )(PH 2 C 6 H 4 CHNCH 2 −) 2 -κ 4 P,N,N,P] + (4 DFT ) to an imine carbon on the ligand to produce the amide complex trans-[Fe(CO)(OC(CH 3 ) 2 )(PH 2 C 6 H 4 CHNCH 2 CH 2 NCH 2 C 6 H 4 PH 2 -κ 4 P,N,N,P)] + (5 DFT acet ) followed by liberation of acetone to afford 5 DFT . Two energetically similar pathways have been proposed in which deprotonation of the PNNP ligand of 5 DFT by strong base produces the experimentally observed ferraaziridinido complex Fe(CO)(PH 2 C 6 H 4 CH NCH 2 CH 2 NCHC 6 H 4 PH 2 )-κ 5 P,N,C,N,P (3 DFT ) or the square-pyramidal Fe(0) complex Fe(CO)(PH 2 C 6 H 4 CHNCH 2 −) 2κ 4 P,N,N,P (7 DFT ). Protonation of 3 DFT by free isopropyl alcohol produces the ferraaziridine complex 2 DFT . Nuclear magnetic resonance and infrared spectroscopy data show that during the transfer hydrogenation of acetophenone catalyzed by 1 in basic isopropyl alcohol, free ligand is observed along with one major iron-containing species identified as 3. On the basis of our calculations of relative free energies and a CO scale factor, we predict that 2 is easily deprotonated to form the electron-rich iron complex 3 and the square-pyramidal Fe(0) complex 7, which are responsible for the two observed CO stretches below 1900 cm −1 in catalytic mixtures. Mass balance studies indicate that the catalytically active species is not observable by NMR. Although 2 and 3 are poor transfer hydrogenation catalysts, we present experimental and theoretical evidence that ligand folding/ distortion is feasible.

The reactivity of the ruthenium−amido bond in RuH(NH2CMe2CMe2NH)(PPh3)2 (1) toward weak acids HX and the influence of the X group on the catalytic activity of the resulting complex are explored here. Complex 1 reacts with the weak acids HX (X = OPh, 4-SC6H4OMe, OPPh2, OP(OEt)2, CCPh, NCCHCN, CH(COOMe)2) to form complexes of the type RuHX(tmen)(PPh3)2 (tmen = 2,3-diamino-2,3-dimethylbutane). The complexes with X = PhOH···OPh, 4-SC6H4OMe, OP(OEt)2, CCPh, CH(COOMe)2 have been characterized by X-ray crystallography. The X group is situated trans to the hydride in all cases and is bonded to ruthenium via the donor atoms O, S, P, C, and O, respectively. The phenol in the phenoxide adduct RuH(PhOH···OPh)(tmen)(PPh3)2 bridges via hydrogen bonds between the alkoxide oxygen and an amino hydrogen to form a six-membered RuO···HO···HN ring. One carbonyl oxygen of the malonate bonds to the Ru, while the other accepts a hydrogen bond from an amino hydrogen. The analogous complexes RuHX(dach)(PPh3)2 (dach = (R,R)-1,2-diaminocyclohexane) were synthesized by the reaction of RuHCl(dach)(PPh3)2 (2) with an equimolar amount of potassium tert-butoxide and HX. For all of the complexes the Ru−H vibrational frequency and the 1H NMR chemical shift of Ru−H correlate with the electronegativity of the trans atom X. The amido complex 1 and the complexes with X = CH(COOMe)2 and OPh are active catalysts for the Michael addition of dimethyl malonate to 2-cyclohexen-1-one. RuH(NCCHCN)(tmen)(PPh3)2 reacts with the Michael acceptor 2-cyclohexen-1-one to give RuH(NCC(C6H9O)CN)(tmen)(PPh3)2, a trapped Michael adduct that has been characterized by X-ray crystallography. On the basis of these observations a catalytic cycle for the Michael addition reactions is proposed that involves the addition of the C−H bond of the Michael donor to the Ru−N bond followed by attack on the Michael acceptor and elimination of the Michael adduct, possibly by a 1,3-proton migration as observed for the malononitrile adduct. Only the complexes with X = H, CCPh are catalysts or precatalysts for the hydrogenation of neat acetophenone to 1-phenylethanol in the absence of added base under 10 atm of H2 at 20 °C. Evidence is provided that the phenylacetylide complexes are precatalysts that are converted to the active trans-dihydride catalysts (X = H).