Calcium Tetraalkylaluminate and Tetramethylgallate Complexes Supported by the Bulky Scorpionate Ligand TptBu,Me

A series of heteroleptic calcium complexes supported by the superbulky scorpionate ligand tris(3-tBu-5-Me-pyrazolyl)­borato (TptBu,Me) was synthesized and characterized comprehensively. Tetramethylaluminate complex (TptBu,Me)­Ca­(AlMe4) was obtained from either [Ca­(AlMe4)2]n and KTptBu,Me according to a salt metathesis protocol or via amide elimination from (TptBu,Me)­Ca­[N­(SiMe3)2] with AlMe3. Using the amide-elimination approach and AlEt3 gave the corresponding tetraethylaluminate complex (TptBu,Me)­Ca­(AlEt4). Treatment of (TptBu,Me)­Ca­(AlMe4) with the Lewis bases thf and 4-(dimethylamino)­pyridine (dmap) afforded the donor-coordinated species (TptBu,Me)­Ca­(AlMe4)­(thf)2 and (TptBu,Me)­Ca­(AlMe4)­(dmap), respectively. While in the absence of donor molecules the tetramethylaluminato ligand is coordinated in a η2 fashion, the thf and dmap adducts exhibit a η1-coordinated AlMe4 ligand in the solid state. Our investigations did not point at the occurrence of any donor-induced cleavage of the Ca–AlMe4 unit toward putative [Ca]–Me species. This was also true for the corresponding tetramethylgallate complex (TptBu,Me)­Ca­(GaMe4), which was accessed via a donor-assisted aluminate/gallate exchange or amide elimination.