Serena Detti

Comparative neutron and X-ray study of [PPN][HIr4(CO)9(μ-Ph2PCH2PPh2)]

Abstract The structure of this tetranuclear iridium cluster featuring a terminal Ir–H bond has been investigated by neutron crystallography using the D19 diffractometer at the Institut Laue Langevin in Grenoble. The structure, which is stabilized by numerous C–H⋯O=C hydrogen bonds, has no π–π stacking. The neutron study described here resolves a difficulty encountered in previous X-ray work where it proved impossible to locate reliably the position of hydrogen in the presence of heavy iridium atoms. Neutron crystallography offers unique advantages for this type of problem and in this case has provided the first reliable value for a terminal Ir–H distance of 1.618(14) Å and an intramolecular H–H contact of 2.40(2) Å.

Crystal structure and fluxional behaviour in solution of [Rh4(CO)6(µ-Me2PCH2PMe2)3]Electronic supplementary information (ESI) available: regression of the Eyring plot of [Rh4(CO)6(µ-Me2PCH2PMe2)3] as measured by 13C–NMR between 169 and 293 K in CD2Cl2. 31P–NMR spectra of [Rh4(CO)6(µ-Me2PCH2PMe2)3] in CD2Cl2 at three different temperatures. See http://www.rsc.org/suppdata/dt/b2/b210986g/

[Rh-4 (CO)(6) (mu-Me2PCH2PMe2)(3)], the first example of a hexasubstituted derivative of Rh-4(CO)(12), has a ground state geometry in the solid state and in solution of C-s symmetry with four edge-bridging carbonyls and with each diphosphine ligand bridging one edge of the same Rh-3 face. The result is an imbalance of the formal electron count at two rhodium atoms. As observed by C-13- and P-31-NMR, the mobility of the ligands is restricted to one mu-CO eta-CO site exchange which astonishingly does not average dynamically the electron count on all four metal atoms.

Intramolecular dynamics of [Rh4(CO)6(μ-PPh2)4] in solution

A 103Rh, 31P and 13C NMR study of [Rh4(CO)6(μ-PPh2)4] in CD2Cl2 indicates that the strongly bonded, bridging, anionic ligand PPh2− takes part in the site exchange of the carbonyl ligands and is actually mobile about the metallic surface of this cluster compound.

SYNTHESIS OF PROTONATED CARBOXYLATO AND TRIFLUOROMETHANESULFONATO DERIVATIVES OF VANADIUM(II) BY REDOX REACTIONS ON BIS(MESITYLENE)-VANADIUM(0)

Bis(mesitylene)vanadium(0), V(mes) 2 , underwent a two-electron redox process in heptane with CF 3 SO 3 H affording the vanadium(II) derivative [V(CF 3 SO 3 ) 2 (CF 3 SO 3 H)], an example of a co-ordination compound containing both the acid and its conjugated base in its composition. The vanadium(0) complex and CF 3 CO 2 H gave a product resulting from a one-electron transfer process, namely [V(mes) 2 ][CF 3 CO 2 ]. This compound, which dissolves unchanged in neat CF 3 CO 2 H–(CF 3 CO) 2 O, evolves to the vanadium(II) derivative [H(thf) n ][V(CF 3 CO 2 ) 3 ] (thf = tetrahydrofuran) by addition of tetrahydrofuran. Deprotonation of the vanadium(II) complexes occurs in the presence of thf or heterocyclic nitrogen bases to form the ionic derivatives [HB][VA 3 ], B = thf or a heterocyclic nitrogen base; A = CF 3 SO 3 or CF 3 CO 2 . The trifluoroacetato derivative [H(thf) n ][V(CF 3 CO 2 ) 3 ] undergoes methylation with CH 2 N 2 to the vanadium(II) ester adduct [V(CF 3 CO 2 ) 2 (CF 3 CO 2 CH 3 )], and is oxidized to the vanadium(III) trifluoroacetato derivatives [V(CF 3 CO 2 ) 3 ] and [V(CF 3 CO 2 ) 2 C 14 H 8 O 2 ] by benzoyl peroxide (or dioxygen) and 9,10-phenanthrenedione, respectively.

Bis(diphosphino)methanide and hydride derivatives of Ir4(CO)12

The reaction of [Ir4(CO)10(μ-(Ph2P)2CH2)] with dried KOH forms [Ir4(CO)10(μ-(Ph2P)2CH)]− which subsequently converts into [Ir4(CO)9(μ3-(Ph2P)2CH)]−, a rare example of an Ir cluster with an Ir–C bond (average 2.274(8) A). The same reaction with the weaker base 1,8-diazobicyclo[5.4.0]undec-7-ene or with K2CO3 in wet CH2Cl2 under CO affords the anion [HIr4(CO)9(μ-(Ph2P)2CH2)]−, a hydride-cluster with an unusually long Ir–H distance (2.08(6) A at 90 K). Intramolecular CO scrambling is observed in CD2Cl2 solution above 200 K, preserving the terminal–axial position of the hydride ligand.