New d⁴dihydrides of Ru(iv) and Os(iv) with π-donor ligands: M(H)₂(chelate)(PⁱPr₃)₂with chelate = ortho-XYC₆H₄with X, Y = O, NR; R = H or CH₃

Abstract

The synthesis and characterization of Ru(H) 2 (ortho-OC 6 H 4 E)L 2 (L ¼ P i Pr 3 , E ¼ NH, O) show these to be dihydrides with a nonoctahedral structure. The former compound reacts with H 2 to give Ru(H) 3 (OC 6 H 4 NH 2 )L 2 , which has the ability to hydrogenate t BuHCQCH 2 . Osmium analogs are available from Os(H) 3 ClL 2 , and the mono-N-methyl example Os(H) 2 [N(Me)C 6 H 4 NH]L 2 shows inequivalent hydrides by 1 H NMR at 20 1C. It exchanges with D 2 faster into the NH site than into the OsH sites. Triflic acid protonates Os(H) 2 [N(Me)C 6 H 4 NH]L 2 at the metal to give a trihydride. Catechol protonates Os(H) 2 [N(Me)C 6 H 4 NH]L 2 to displace the ortho-diamine to give Os(H) 2 (OC 6 H 4 O)L 2 . The collective evidence is consistent with a dianionic, not a quinoid oxidation state for the chelate ligands and a d 4 , six-coordinate potential energy surface, often with low barriers between alternative non-octahedral structures. Experimental GeneralAll manipulations were performed using standard Schlenk techniques or in an argon-filled glovebox unless otherwise noted. Solvents were distilled from Na, Na/benzophenone, P 2 O 5 , or CaH 2 , degassed prior to use, and stored over 4 A molecular sieves in airtight vessels. Lithium salts o-C 6 H 4 (OH) OLi and o-C 6 H 4 (NH 2 )OLi were prepared by reacting n BuLi with catechol (see below) and 2-aminophenol (1 : 1 molar ratio) in benzene, respectively, then isolated as white solids by removal of the volatiles in vacuo. [RuHCl(P i Pr 3 ) 2 ] 2 , 17 written in this section as a monomer to clarify reaction stoichiometries, and Os(H) 3 Cl(P i Pr 3 ) 2 18 were prepared as previously reported; all other reagents were used as received from commercial vendors. 1 H NMR chemical shifts are reported in ppm relative to protio impurities in the deutero solvents. 31 P NMR spectra are referenced to an external standard of 85% H 3 PO 4 (0 ppm).

Hydrogenolysis of β-O-4 lignin model dimers by a ruthenium-xantphos catalyst

“…The ESI/MS spectrum and elemental analysis support the formulation of 19, whereas the NMR spectra in CD 2 Cl 2 (four, equal intensity 1 H singlets for the Me groups, and two 1 : 1 31 P{ 1 H} singlets at δ 49.9 and 55.1) imply the presence of two isomers in solution; these are most likely species with cis-and trans-P atoms of tridentate xantphos. The closest reported analogue of 19 is cis, trans-Ru(CO) 2 (P i Pr 3 ) 2 (OC 6 H 4 O) which has equivalent trans P-atoms showing a δ P singlet resonance at 43.4 (in C 6 D 6 ),37 similar to the values for 19.…”

Preparation of Half-Sandwich Osmium Complexes by Deprotonation of Aromatic and Pro-aromatic Acids with a Hexahydride Brønsted Base

“…The most noticeable feature of the complex are the H(01)–Os–H(02) and H(02)–Os–H(03) angles of 58.1(5)° and 62.1(15)°, respectively, which markedly deviate from 90°. It is well known that the octahedral geometry is not favorable for heavy metal d 4 complexes, which prefer to be diamagnetic. ,, These complexes therefore undergo a distortion that destabilizes one orbital from the t 2g set and simultaneously stabilizes some occupied orbitals. The distortion is typical for OsH 3 X(PR 3 ) 2 complexes and partially cancels the electron deficiency at the metal, which receives additional electron density from the hydrides via stronger σ-bonds and from one lone pair of X via a π-bond .…”

Analysis of the Aromaticity of Osmabicycles Analogous to the Benzimidazolium Cation

“…We reasoned that the chloride ligands of complex OsH 2 Cl 2 (P i Pr 3 ) 2 ( 1 ) could be easily replaced by the chelate nitrogen donor ligand and, in fact, the treatment at room temperature of dichloromethane suspensions of 1 with 1.2 equiv of 1,2-phenylenediamine in the presence of 4.0 equiv of triethylamine leads to OsH 2 (κ-N,N- o -HNC 6 H 4 NH)(P i Pr 3 ) 2 ( 2 ), which is isolated in 73% yield, according to eq . The presence of an o -benzoquinonediimine ligand in 2 was initially confirmed by the 1 H NMR spectrum of the obtained orange solid in dichloromethane- d 2 , at room temperature. The spectrum contains a NH resonance at 8.01 ppm.…”