Probing the Effect of the Ligand X on the Properties and Catalytic Activity of the Complexes RuHX(diamine)(PPh₃)₂ (X = OPh, 4-SC₆H₄OCH₃, OPPh₂, OP(OEt)₂, CCPh, NCCHCN, CH(COOMe)₂; diamine = 2,3-Diamino-2,3-dimethylbutane, (R,R)-1,2-Diaminocyclohexane)

Abstract

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).

CNN Pincer Ruthenium Catalysts for Hydrogenation and Transfer Hydrogenation of Ketones: Experimental and Computational Studies

“…It is worth noting that alkoxide and phenoxide Ru complexes with a NH function were isolated as alcohol and phenol adducts and that the corresponding X‐ray structures showed a six‐membered RuO ⋅⋅⋅ HO(R) ⋅⋅⋅ HN cycle. The corresponding reference compounds are [Ru(CO) 2 {OC(CF 3 ) 2 CH 2 NH 2 } 2 ] ⋅ (CH 3 OH) 2 ,46 [RuH(CO)(O i Pr)(HN(C 2 H 4 P i Pr 2 ) 2 )] ⋅ ( i PrOH),42 and [RuH(OPh)(H 2 NCMe 2 CMe 2 NH 2 )(PPh 3 ) 2 ] ⋅ PhOH 47…”

Iron Group Hydrides in Noyori Bifunctional Catalysis

“… A condensed overview of representative ruthenium hydride complexes prepared starting from RuHCl(PPh 3 ) 3 ; more details can be found later in the text. Reaction 1a: D‐NH 2 represents a variety of bidentate ligands where D‐ is an amine or 2‐pyridyl donor with a group linking to the NH 2 ; X = BH 4 , or H ‐ from H 2 /base; Reaction 2a: PAr 2 ‐PAr 2 = BINAP37 , 40–43 or BINOP;44,45 and D‐NH 2 represents a variety of bidentate ligands with D = amine, pyridyl or phosphine donor moiety; Reaction 3a: PPh 2 ‐NH 2 represents a variety of β‐aminophosphine bidentate ligands (the ligand PNOR is shown); 42,43 , 46 Reaction 4a: PPh 2 ‐N‐N‐PPh 2 is a tetradentate ligand with diphenylphosphino and imine or amine donors (the ligand derived from ( R,R )‐diaminocyclohexane is shown) 47–49…”

A Green Chemistry Approach to Asymmetric Catalysis: Solvent-Free and Highly Concentrated Reactions

“…Related catalysts gave lower enantioselectivities. 265 In the asymmetric hydrogenation of imines, catalyst derived from C gave up to 92% enantioselectivity with the n-Bu imine of acetophenone and was about an order of magnitude more active than the BINAP catalysts formed from A and B.…”