John S. Ricci

Single-crystal X-ray and neutron diffraction structure determination and inelastic neutron scattering study of the dihydrogen complex trans-[Ru(H2)(H)(dppe)2][BPh4]

Abstract The structure of the complex trans -[Ru( η 2 -H 2 )(H)(dppe) 2 ][BPh 4 ]( 1 ),dppe = PPh 2 CH 2 CH 2 PPh 2 , has been determined by single-crystal X-ray diffraction at 123 K and neutron diffraction at 12 K. The core of the complex has a distorted octahedral geometry about ruthenium with the dihydrogen ligand trans to hydride and eclipsing a trans -Pue5f8Ruue5f8P axis that is bent away front the hydrogens with a Pue5f8Ruue5f8P angle of 167.9(4)°. The crystallographically determined H-H distance is 0.83(8) (X-ray) or 0.82(3) (neutron) A. The latter value, where corrected for the shortening caused by the torsional libration of the H 2 ligand, increases to about 0.94 A. The long Ruue5f8(H 2 ) distance of 1.81(2) A (neutron), compared to the terminal hydride to ruthenium distance of 1.64(2) A (neutron), is consistent with the lability of the dihydrogen ligand, which is partially lost from the crystal by treatment with vacuum. The analogous iron complex trans-[Fe(η) 2 -H 2 )(H)(dppe) 2 [BPh 4 ]( 2 ) has similar features except that the Feue5f8H(H 2 ) distances are much shorter and the H 2 ligand is correspondingly less labile. An inelastic neutron scattering study of the powder of 1 at 5 K reveals two broad inelastic peaks flanking the elastic peak. With the assumption that the dihydrogen librates in a double-minimum potential, the barrier to dihydrogen reorientation is calculated to be 1.0 to 1.4 kcal mol − , depending upon which of the Hue5f8H distances is used. This barrier is less than that for the iron analog, determined for its BF 4 salt, therefore suggesting that there may be less d π → σ ∗ backbonding in 1 than 2 .

Synthetic and reactivity studies of some asymmetric dinuclear platinum(II) monohydrido-bridged cations. The neutron diffraction structure of [(Pet3)2(Ph)Pt(μ-H)PtH(PEt3)2][BPh4]

Abstract The complexes [(PEt 3 ) 2 (Ar)Pt(μ-H)PtH(PEt 3 ) 2 ][BPh 4 ] (Ar=Ph,2,4-Me 2 C 6 H 3 , 2,4,6-Me 3 C 6 H 22 ) were prepared and characterized. Multinuclear, multidimensional NMR studies of these complexes show that, in solution, (i) they exist in rapidly intercoverting conformers which retainn the bent Pt(μ-H)PtH moieties found in the solid state, (ii) the coordination at each platinum atom is square planar, (iii) the two coordination planes are perpendicular to each other and (iv) the aryl group is perpendicular to the coordination plane of the platinum atom to which it is bonded. The complex [PEt 3 ) 2 Pt(μ-H)PtH(PEt 3 ) 2 ][BPh 4 ] does not react with C 2 H 4 and CH 2 :CH·CO 2 Me. At −60°C or above, [(PEt 3 ) 2 (Ph)Pt(μ-H)PtH(PEt 3 ) 2 )][BPh 4 ] reacts with CO giving the platinum(II) cations trans-[ PtX(CO)(PEt 3 ) 2 ]( Ph ) ∗ ( X = H and Ph ), and [PtH(PEt 3 ) 3 ] + and the platinum(0) carbonyl cluster [Pt 4 (μ-CO) 3 ) 4 ]. The cluster structure of I(PEt 3 ) 2 (Ph)·Pt(μ-H)PtH(PEt 3 ) 2 ][BPh 4 , obtained by neutron diffraction, shows that the Pt-H-Pt bond angle in this cation is 125(1)° indicating that the interaction between these three atoms is weak.

Transition metal methylene complexes: LXVII. Neutron diffraction study of μ-propylidene(2)-bis[carbonyl(η5-pentamethylcyclopentadienyl)rhodium-(RhRh)], [μ-C(CH3)2][{η5-C5(CH3)5}Rh(CO)]2, at 20 K

Abstract The title compound 3 , is prepared by reaction of [(μ-CO)(η 5 -C 5 Me 5 )Rh] 2 , 1 , with N 2 =CMe 2 , 2 . A neutron diffraction study of the structure of 3 at 20 K reveals a normal dimeric structure with approximate C 2 molecular symmetry and a Rhue5f8Rh single bond (2.66 A). The geometry of the bridging propylidene ligand shows no exceptional features that might be connected with the unusual photolysis behavior of 3 , wherein a diamagnetic material with complex 1 H- and 13 C-NMR spectra is formed. Crystallographic data: a 16.856(3), b 15.978(5), c 18.730(11) A, β 107.50(2)°, Z = 8, space group P 2 1 / c (No. 14), R ( F 2 ) ue5fb 0.141 for 8514 neutron data.