Octahedral perfluoroalkyl complexes of Ir(III) formed by oxidative addition of perfluoroalkyl iodides to Ir(acac)(CO)2

Oxidative addition of primary, secondary, or benzylic perfluoroalkyl iodides (RF–I) to the phosphine free Ir(I) precursor Ir(acac)(CO)2 1 (acac = 2,4-pentanedionato) proceeds smoothly to afford octahedral Ir(III) products Ir(acac)(I)(RF)(CO)2, A combination of X-ray crystallographic studies and solution spectroscopy shows that these products are the result of overall trans-addition of the C–I bond to iridium, probably a result of thermodynamic control; evidence for a kinetic product resulting from net cis-addition is obtained in one case. Treatment of the Ir(III) compounds with AgOTf (Tf = CF3SO3) illustrates that the iodo ligand is replaced by triflate with retention of stereochemistry at Ir. The resulting triflate complexes are inert to displacement by H2O or H2. The Ir(III) products exhibit very high CO stretching frequencies in the IR, indicating that the CO ligands may be non-classical. A quantitative estimation of the degree of backbonding to the CO ligands in these compounds, and a comparison of the π-acceptor properties of CO and fluoroalkyl ligands, is made using an approach based on Density Functional Theory (DFT) and Natural Bond Orbital analyses.Key words: iridium, fluoroalkyl, oxidation, carbonyl, DFT.

Linear Metal−Metal-Bonded Tetranuclear M−Mo−Mo−M Complexes (M = Ir and Rh): Oxidative Metal−Metal Bond Formation in a Tetrametallic System and 1,4-Addition Reaction of Alkyl Halides

Reaction of Mo2(pyphos)4 (1) with [MCl(CO)2]2 (M = Ir and Rh) afforded linear tetranuclear complexes of a formula Mo2M2(CO)2(Cl)2(pyphos)4 (2, M = Ir; 3, M = Rh). X-ray diffraction studies confirmed that two "MCl(CO)" fragments are introduced into both axial sites of the Mo2 core in 1 and coordinated by two PPh2 groups in a trans fashion, thereby forming a square-planar geometry around each M(I) metal. Treatment of 2 and 3 with an excess amount of tBuNC and XylNC induced dissociation of the carbonyl and chloride ligands to yield the corresponding dicationic complexes [Mo2M2(pyphos)4(tBuNC)4](Cl)2 (5a, M = Ir; 6a, M = Rh) and [Mo2M2(pyphos)4(XylNC)4](Cl)2 (7, M = Ir; 8, M = Rh). Their molecular structures were characterized by spectroscopic data as well as X-ray diffraction studies of BPh4 derivatives [Mo2M2(pyphos)4(tBuNC)4](BPh4)2 (5b, M = Ir; 6c, M = Rh), which confirmed that there is no direct sigma-bonding interaction between the M(I) atom and the Mo2 core. The M(I) atom in 5 and 6 can be oxidized by either 2 equiv of [Cp2Fe][PF6] or an equimolar amount of I2 to afford Mo(II)2M(II)2 complexes, [Mo2M2(X)2(tBuNC)4(pyphos)4]2+ in which two Mo-M(II) single bonds are formed and the bond order of the Mo-Mo moiety has been decreased to three. The Ir(I) complex 5a reacted not only with methyl iodide but also with dichloromethane to afford the 1,4-oxidative addition products [Mo2Ir2(CH3)(I)(tBuNC)4(pyphos)4](Cl)2 (13) and [Mo2Ir2(CH2Cl)(Cl)(tBuNC)4(pyphos)4](Cl)2 (15), respectively, although the corresponding reactions using the Rh(I) analogue 6 did not proceed. Kinetic analysis of the reaction with CH3I suggested that the 1,4-oxidative addition to the Ir(I) complex occurs in an SN2 reaction mechanism.

Adding a new dimension to the investigation of platinum-mediated arene C-H activation reactions using 2D NMR exchange spectroscopy. Dynamics of Pt(II) phenyl/benzene site exchange

Protonation of (N-N)PtPh(2) (1; N-N = diimine ArN=CMe-CMe=NAr with Ar = 2,6-Me(2)C(6)H(3) (a), 2,4,6-Me(3)C(6)H(2) (b), 4-Br-2,6-Me(2)C(6)H(2) (c), 3,5-Me(2)C(6)H(3) (d), and 4-CF(3)C(6)H(4) (e)) in the presence of MeCN at ambient temperature generates (N-N)Pt(Ph)(NCMe)(+) (2). At -78 degrees C, protonation of 1a yielded (N-N)PtPh(2)(H)(NCMe)(+) (3a), which produced benzene and 2a at ca. -40 degrees C. Protonation of 1a-e in CD(2)Cl(2)/Et(2)O-d(10) furnished (N-N)Pt(C(6)H(5))(eta(2)-C(6)H(6))(+) (4a-e). The pi-benzene complexes 4a-c, sterically protected at Pt, eliminate benzene at ca. 0 degree C. The sterically less protected 4d-e lose benzene already at -30 degrees C. SST and 2D EXSY NMR demonstrate that phenyl and pi-benzene ligand protons undergo exchange with concomitant symmetrization of the diimine ligand, most likely via oxidative insertion of Pt into a C-H bond of coordinated benzene. The kinetics of the exchange processes for 4a-c were probed by quantitative EXSY spectroscopy, resulting in DeltaH() of 70-72 kJ mol(-1) and DeltaS of 37-48 J K(-1) mol(-1). A large, strongly temperature-dependent H/D kinetic isotope effect (9.7 at -34 degrees C; 6.9 at -19 degrees C) was measured for the dynamic behavior of 4a versus 4a-d(10), consistent with the proposed pi-benzene C-H bond cleavage. The fact that the pi-benzene complex 4a is thermally more robust in the absence of MeCN than is the Pt(IV) hydridodiphenyl complex 3a in the presence of MeCN agrees with the notion that arene elimination from Pt(IV) hydridoaryl complexes occurs via Pt(II) pi-arene intermediates that eliminate the hydrocarbon associatively, in this case, promoted by MeCN. Compounds 1a, 1b, 1d, 2a, and 2b have been crystallographically characterized.