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Ligand backbone alkylation of the complex [Cr(CO)4(dppm)] (dppm = bis(diphenylphosphino)methane) with alkyl iodides yields the C-substituted dppm ligand complexes [Cr(CO)4{Ph2PCH(R)PPh2}] (R = methyl, n-hexyl, benzyl). Activation of these complexes via one-electron oxidation with Ag[(Al(OC4F9)4] and CO removal with triethylaluminium, or (in the case of R = methyl) by in situ treatment of the free ligand with a chromium salt and modified methyl alumoxane (MMAO), leads to catalysts showing some selectivity for ethylene trimerization and tetramerization. NMR spectroscopic studies of the parent dppm or [Cr(CO)4(dppm)] compounds suggest that ligand deprotonation and decomplexation may be the cause of the surprisingly poor catalytic performance of these specific derivatives.

Rhodium and iridium complexes with N-heterocyclic carbenes (NHC) functionalized with neutral or anionic indenyl and fluorenyl groups are reported. In the complexes the ligands adopt monodentate, bidentate or bridging bonding modes with the NHC group σ-bonded and the fluorenyl or indenyl functionalities either dangling or coordinated to the metal with various hapticities (η1, η3 and η5). Metallation of the C–H bond of the alkylene linker in the ligand has also been observed. Catalytic studies on the bidentate RhI complex 6 show that it is weakly active for the hydroformylation of 1-octene with poor linear selectivity, but it shows slightly lower activity than the standard Monsanto system for the carbonylation of methanol.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Synthetic, structural, and catalytic studies of a series of molybdenum complexes with the tridentate “SNS” ligands bis(decylthioethyl)amine and bis(ethylthioethyl)amine are reported. Complexes with a range of molybdenum oxidation states {(0), (III), and (IV)} have been accessed synthetically in high yields from readily synthesized starting materials. The formation of an unexpected dimeric molybdenum(I) structure is also reported. Where possible, the complexes have been converted to salts of the weakly coordinating tetrakis(perfluoro-tert-butoxy)aluminate anion. The complexes have been screened for ethylene oligomerization activity with a number of aluminum cocatalysts.

Dimethylindenyl-functionalized N-heterocyclic carbene complexes of titanium(IV), titanium(III), zirconium(IV), and vanadium(III) were prepared from potassium indenylcarbenes by salt elimination reactions. X-ray diffraction studies revealed that in the complexes the ligand adopts a bidentate coordination mode. Alkanolysis of a dimethylindene-functionalized imidazolium salt with Y(CH2SiMe3)3(THF)2 gave rise to a dimeric yttrium bromo alkyl in which the ligand adopts a bidentate coodination mode. Aminolysis of the fluorene-functionalized imidazolium salts with {[Cr(N(SiMe3)2)2(THF)2} led to chromium(II) complexes in which the ligand adopts a monodentate binding mode via the N-heterocyclic carbene end with dangling fluorene groups.

The new N-heterocyclic carbene ligands functionalized with indenyl and fluorenyl groups, 1-[ind-(CH2)2]-NHC, (Ind-NHC)-, and 1-[fl-(CH2)2]-NHC, (Fl-NHC)-, where ind = 1-indenyl, fl = 9-fluorenyl, NHC = 3-DiPP-imidazol-2-ylidene, DiPP = 2,6-Pri2-C6H3, serve as versatile building blocks of Ti(III) and V(III) complexes.