Coordination chemistry of aluminum, gallium, and indium at transition metals

The surge in the interest in the coordination chemistry of aluminum, gallium, and indium at transition metals is attributed to impulses that have only recently become effective and which originate from two different motivations. One stems from the understanding that organometallic compounds are potential precursors for applications in the field of new materials, and the other from the resurgence of the chemistry of low-valent Group 13 metals (earth metals), which is currently being extended to the coordination chemistry at d-block metals. A special highlight is the compound [Ni(InR)₄] (R = C(SiMe₃)₃), a first example for the existence of complexes that are homoleptic with respect to the earth metal as ligator. This compound and the complexes [{CpNi-AlCp*}₂], [Cp*Al-Fe(CO)₄], and [(CO)₄Fe-GaAr*] (Ar* = 2,6-bis(2,4,6-triisopropylphenyl)phenyl) illustrate the lively development and the current trends in this field. A series of reports on the quantum chemical description of the bonding have originated not least in connection with the debate on the postulated Fe-Ga triple bond in the complex [(CO)₄Fe- GaAr*]. According to these theoretical papers the very polar M-E bonds of the different types of complexes fit well into the Lewis donor/acceptor concept for metal-ligand bonds. Multiple bonds in the traditional sense play only a minor role. Remarkably little is known about the reactivity of the M-E complexes if one disregards the chemistry relevant for metal-organic chemical vapor deposition (MOCVD).