The fifteen‐membered NNNNN macrocycle Me5PACP (Me5PACP=1,4,7,10,13‐pentamethyl‐1,4,7,10,13‐pentaazacyclopentadecane) stabilized the [CaH]+ fragment as a dimer with a distorted pentagonal bipyramidal coordination geometry at calcium. The hydride complex was prepared by protonolysis of calcium dibenzyl with the conjugate acid of Me5PACP followed by hydrogenolysis or treating with nOctSiH3 of the intermediate calcium benzyl cation. The calcium hydride catalyzed the hydrogenation and hydrosilylation of unactivated olefins faster than the analogous calcium complex stabilized by the twelve‐membered NNNN macrocycle Me4TACD (Me4TACD=1,4,7,10‐tetramethyl‐1,4,7,10‐tetraazacyclododecane). Kinetic investigations indicate that higher catalytic efficiency for the Me5PACP stabilized calcium hydride is due to easier dissociation of the dimer in solution when compared to the Me4TACD analogue.

A trinuclear strontium hydride [(Me4TACD)3Sr3(µ2-H)4(thf)][B(C6H3-3,5-Me2)4]2 (Me4TACD = 1,4,7,10-tetramethyl-tetraazacyclododecane) and a mixed calcium strontium hydride [(Me4TACD)2CaSr(µ-H)2(thf)]2+ were isolated by hydrogenolysis of cationic benzyl precursors. A solution of [(Me4TACD)2CaSr(µ-H)2(thf)][B(C6H3-3,5-Me2)4]2 shows hydride ligand...

The molecular strontium hydride [(MeTACD)Sr(μ-H)][SiPh] (2) was isolated as the dark red benzene solvate 2·CH in 69% yield from the reaction of [Sr(SiPh)(thf)] (1') with (MeTACD)H (1,4,7-trimethyl-1,4,7,10-tetraazacyclododecane). This reaction can be considered as a redox process, with the Brønsted acidic amine proton in (MeTACD)H transformed into the hydride by the anion [SiPh]. Trace amounts of water resulted in the formation of [(MeTACD)Sr(μ-H)(μ-OH)][SiPh] (2*), which cocrystallized with 2. Single-crystal X-ray diffraction of 2 revealed a substitutional disorder of a bridging hydride with a hydroxide ligand. Hydride complex 2 was also obtained by hydrogenolysis of [(MeTACD)Sr(SiPh)] (3), although pure 3 proved difficult to isolate. In the presence of a 2-fold excess of (MeTACD)H, the reaction with disilyl 1' gave [(MeTACD)SiPh] (4). Complex 2 underwent facile H/D exchange with D (1 bar), with the anion [SiPh] decomposing concurrently. In the reaction of 2 with 1,1-diphenylethylene (DPE), the anion [SiPh] was added to the C═C bond in DPE to give [(MeTACD)SrH][PhCCHSiPh] (5), whereas the cationic cluster [(MeTACD)SrH] remained unchanged. 9-Fluorenone underwent one-electron reduction with 2 to give the paramagnetic ketyl complex [{(MeTACD)H}Sr(OCH)(thf)] (6). These strontium compounds are structurally similar to the lighter calcium congeners, but more reactive, in particular with regard to fast H/D exchange and [SiPh] anion decomposition. DFT studies on the cationic hydride clusters suggest a more pronounced covalent character for strontium compared to calcium. Disilyl 1, strontium diketyl 6, and the calcium congener of 6, [{(MeTACD)H}Ca(OCH·)] (10), were also characterized by X-ray diffraction.

The cationic benzyl complex [(Me 4 TACD)Sr-(CH 2 Ph)][A] (Me 4 TACD = 1,4,7,10-tetramethyltetraazacyclododecane; A = B(C 6 H 3 -3,5-Me 2 ) 4 ) reacted with two equivalents of phenylsilane to give the bridging hexahydridosilicate complex [(Me 4 TACD) 2 Sr 2 (thf) 4 (μ-k 3 : k 3 -SiH 6 )][A] 2 (3 a). Rapid phenyl exchange between phenylsilane molecules is assumed to generate monosilane SiH 4 that is trapped by two strontium hydride cations [(Me 4 TACD)SrH(thf) x ] + . Complex 3 a decomposed in THF at room temperature to give the terminal silanide complex [(Me 4 TACD)Sr(SiH 3 )-(thf) 2 ][A], with release of H 2 . Upon reaction with a weak Brønsted acid, CO 2 , and 1,3,5,7-cyclooctatetraene SiH 4 was released. The reaction of a 1 : 2 mixture of cationic benzyl and neutral dibenzyl complex with phenylsilane gave the trinuclear silanide complex [(Me 4 TACD) 3 Sr 3 (μ 2 -H) 3 (μ 3 -SiH 3 ) 2 ]-[A], while n OctSiH 3 led to the trinuclear (noctyl)pentahydridosilicate complex [(Me 4 TACD) 3 Sr 3 (μ 2 -H) 3 (μ 3 -SiH 5 n Oct)][A].