Heterometallic Polyhydride Complexes Containing Yttrium Hydrides with Different Cp Ligands: Synthesis, Structure, and Hydrogen-Uptake/Release Properties

A new family of Y4/M2 and Y5/M heterobimetallic rare-earth-metal/d-block-transition-metalpolyhydride complexes has been synthesized. The reactions of the tetranuclear yttriumoctahydride complex [{CpY(-H)2}4(thf)4] (Cp=C5Me4H, 1-C5Me4H) with oneequivalent of Group-6-metalpentahydride complexes [Cp*M(PMe3)H5] (M=Mo, W; Cp*=C5Me5) afforded pentanuclear heterobimetallic Y4/Mpolyhydride complexes [{(CpY)4(-H)7}(-H)4MCp*(PMe3)] (M=Mo (2a), W (2b)). UV irradiation of compounds 2a,b in THF gave PMe3-free complexes [{(CpY)4(-H)6(thf)2}(-H)5MCp*] (M=Mo (3a), W (3b)). Compounds 3a,b reacted with oneequivalent of [Cp*M(PMe3)H5] to afford hexanuclear Y4/M2 complexes [{Cp*M(-H)5}{(CpY)4(-H)5}{(-H)4MCp*(PMe3)}] (M=Mo (4a), W (4b)). UV irradiation of compounds 4a,b provided the PMe3-free complexes [(CpY)4(-H)4{(-H)5MCp*}2] (M=Mo (5a), W (5b)). C5Me4Et-ligated analogue [(CpY)4(-H)4{(-H)5Mo(C5Me4Et)}2] (5a) was obtained from the reaction of 1-C5Me4H with [(C5Me4Et)Mo(PMe3)H5]. On the other hand, the reaction of pentanuclear yttriumdecahydride complex [{(C5Me4R)Y(-H)2}5(thf)2] (1-C5Me5: R=Me; 1-C5Me4Et: R=Et) with [Cp*M(PMe3)H5] gave the hexanuclear heterobimetallic Y5/Mpolyhydride complexes [({(C5Me4R)Y}5(-H)8)(-H)5MCp*] (6a: M=Mo, R=Me; 6a: M=Mo, R=Et; 6b: M=W, R=Me). Compound 5a released two molecules of H2 under vacuum to give [(CpY)4(-H)2{(-H)4MoCp*}2] (7). In contrast, compound 6a lost one molecule of H2 under vacuum to yield [{(Cp*Y)5(-H)7}(-H)4MoCp*] (8). Both compounds 7 and 8 readily reacted with H2 to regenerate compounds 5a and 6a, respectively. The structures of compounds 4a, 5a, 6a, 7, and 8 were determined by single-crystal X-ray diffraction.