Reactivity of a Molecular Calcium Hydride Cation ([CaH]+) Supported by an NNNN Macrocycle

The hydride ligand in the cationic calcium hydride supported by a NNNN-type macrocycle, [(Me(4)TACD)(2)Ca-2(mu H)(2)(THF)][BAr4](2) (1; Me(4)TACD = 1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclododecane; THF = tetrahydrofuran; BAr4 = B(C6H3-3,5-Me-2)(4)), shows, in addition to its Bronsted basicity toward weak acids, a pronounced nucleophilicity resulting in nucleophilic substitution or insertion (addition) at a silicon or sp(2) carbon center. Terminal acetylenes RC equivalent to CH (R = SiMe3, cyclopropyl) as well as 1,4-diphenylbutadiene were deprotonated by 1 to give dinuclear complexes [(Me(4)TACD)(2)Ca-2(mu-C equivalent to CR)(2)][BAr4](2) (2a, R = SiMe3; 2b, R = cyclopropyl) and [(Me(4)TACD)(2)Ca-2(mu(2)-eta(4)-1,4-Ph2C4H2)][BAr4](2) (3) with H-2 evolution. The addition reaction with BH3(THF) gave a tetrahydridoborate complex, [(Me(4)TACD)Ca(BH4)(THF)(2)][BAr4] (4), with kappa(2)-H2BH2 coordination in the solid state, suggesting a pronounced Lewis acidic calcium center. The behavior resulting from both Lewis acidity and hydricity becomes apparent in the nucleophilic substitution of fluorobenzene by 1 to give benzene and the dimeric fluoride complex [(Me(4)TACD)(2)Ca-2(mu-F)(2)(THF)][BAr4](2)center dot 2.5THF (5). Analogous nucleophilic substitution reaction is observed for heterofunctionalized organosilanes XSiR3 [X = I, N(SiHMe2)(2), N-3; R = Me-3 or HMe2], which resulted in the formation of calcium complexes [(Me(4)TACD)Ca(X)(THF)(n)][BAr4] (6-8) containing an X ligand along with hydrosilane HSiR3. An insertion reaction by 1 was observed with CO2 and CO to give dinuclear formato complex [(Me(4)TACD)(2)Ca-2(mu-OCHO)(2)][BAr4](2) (9) and cis-enediolato complex [(Me(4)TACD)(2)Ca-2(mu-OCH=CHO)][BAr4](2)center dot 3.5THF (10), respectively. The latter is believed to have been formed as a result of the dimerization of an initially generated formyl or oxymethylene complex, [(Me(4)TACD)Ca(OCH)](+).