No abstract

Os(H)(3)ClL(2) (L = P(i)Pr(3)) reacts at 20 degrees C with vinyl fluoride in the time of mixing to produce OsHFCl([triple bond]CCH(3))L(2) and H(2). In a competitive reaction, the liberated H(2) converts vinyl fluoride to C(2)H(4) and HF in a reaction catalyzed by Os(H)(3)ClL(2). A variable-temperature NMR study reveals these reactions proceed through the common intermediate OsHCl(H(2))(H(2)C=CHF)L(2), via OsClF(=CHMe)L(2) and OsHCl(H(2))(C(2)H(4))L(2), all of which are detected. DFT(B3PW91) calculations of the potential energy and free energy at 298 K of possible intermediates show the importance of entropy to account for their thermodynamic accessibility. Calculations of unimolecular C-F cleavage of coordinated C(2)H(3)F confirms the high activation energy of this process. Catalysis by HF is thus suggested to account for the fast observed reactions, and scavenging of HF with NEt(3) changes the product to exclusively Os(H)(2)Cl(CCH(3))L(2). The analogous reaction of Os(H)(3)ClL(2) with H(2)C=CF(2) produces exclusively OsHFCl(=CCH(3))L(2) and HF, and the latter is again suggested to catalyze C-F scission via the observed intermediates Os(H)(2)Cl(CF(2)CH(3))L(2) and OsHCl(=CFMe)L(2).

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).