114-143.pdf
Transcript
The Arrhenius equation coalescence temperature J. Am. Chem. Soc. 1971, 93, 15, 3587–3591 (5-Cp)2 (1-Cp)2 Ti Metal...
The Arrhenius equation coalescence temperature J. Am. Chem. Soc. 1971, 93, 15, 3587–3591 (5-Cp)2 (1-Cp)2 Ti Metal-Metal Multiple Bonds For M-L bonding Metal-Metal Quadruple Bond Re is 50 pm out of plane of 4Cl atoms Re ….. Re distance in Re Metal = 275 pm (8 e- for two Re3+ atoms) Metal-Metal Triple Bond 2π4δ2δ*2 Configuration Metal-Metal Quintuple Bond (cautiously called – 5 fold bonding) 2π4δ4 Configuration Among the five bonds present between the metal centers, one is a sigma bond, two are pi bonds, and two are delta bonds. The σ-bond is the result of mixing between the dz2 orbital on each metal center. The first π-bond comes from mixing of the dyz orbitals from each metal while the other π-bond comes from the dxz orbitals on each metal mixing. Finally the δ-bonds come from mixing of the dxy orbitals as well as mixing between the dx2−y2 orbitals from each metal. Cr(I), d5 Cr…..Cr = 183.5 pm (quadruple bond = 236.9 pm) All Quintuple bond complexes contain bidentate bridging ligands Acts as “Tweezer” using steric effects so that the M-M can come closer. Some facts about [(Re2)x+(Cl8)]n- Metal-Metal bonds Calculation 24 e- 12x2=24 e- Fe3(CO)12 A (TVE) = 48 B = 54-48 = 6 Total M-M bond = 6/2 = 3 Electrons/metal = 48/3 = 16 Fe Fe Fe Calculate for Co4(CO)12 ; [5-CpMo(CO)2]2 Metal-Metal bonds Calculation Co4(CO)12 A (TVE) = 60 B = 72-60 = 12 Total M-M bond = 12/2 = 6 Calculate for [5-CpMo(CO)2]2 Ir4(CO)12 [5-CpMo(CO)2]2 A (TVE) = 30 B = 36-30 = 6 Total M-M bond = 6/2 = 3 Hoffmann’s symbol `(exact mech unknown!) 2 + CO + H2 + BuO- OXAD & REDUCTIVE ELIMINATION Ph Ti(BH4)3(PMe)2 M-H-Y Y = B, N, Cl, Si, C or F Equatorial BH4- ion Axial PMe3 JACS, 1988, 110, 4977. One bidentate BH4- ion Two monodentate BH4 ions (Agostic B-H bond attached to Ti in a side-on manner Ti-H…B Agostic Interaction Distorted trigonal pyramidal geometry C-H bond energy ~ 400 kJ/mol The possible sequence of functionalization of hydrocarbons begins with coordination of alkane. Titan (moon of Saturn) Liquid methane sea insertion rxn i.e. Decarbonylation
