One of the major limitations to the use of fuel cell systems in vehicular transportation is the lack of hydrogen storage systems that have the required hydrogen storage density and moderate enthalpy of dehydrogenation. Organic liquid H(2) carriers that release H(2) endothermically are easier to handle with existing infrastructure because they are liquids, but they have low storage densities and their endothermicity consumes energy in the vehicle. On the other hand, inorganic solid H(2) carriers that release H(2) exothermically have greater storage densities but are unpumpable solids. This paper explores combinations of an endothermic carrier and an exothermic carrier, where the exothermic carrier provides some or all of the necessary heat required for dehydrogenation to the endothermic system, and the endothermic carrier serves as a solvent for the exothermic carrier. The two carriers can be either physically mixed or actually bonded to each other. To test the latter strategy, a number of chemically bound N-heterocycle:BH(3) adducts were synthesized and in turn tested for their ability to release H(2) by tandem hydrolysis of the BH(3) moiety and dehydrogenation of the heterocycle. To test the strategy of physically mixing two carriers, the hydrolysis of a variety of amine-boranes (H(3)N:BH(3), Me(2)HN:BH(3), Et(3)N:BH(3)) and the catalytic dehydrogenation of indoline were carried out together.
1-(Diphenylphosphino)-2-(dimethylamino)indene (2c) has been prepared in 61% yield and upon exposure to Al 2 O 3 is mostly isomerized to 3-(diphenylphosphino)-2-(dimethylamino)-indene (2d) (2c:2d ≈ 1:3); similarly, 1-(diisopropylphosphino)-2-(dimethylamino)indene (2a) is only partially converted to the corresponding C3 isomer (2b) upon treatment with Al 2 O 3 (2a:2b ≈ 3:1). In contrast, 1-(diisopropylphosphino)indene (6a) has been prepared in 92% yield and is easily converted to 3-(diisopropylphosphino)indene (6b) on passing over Al 2 O 3 ; 0.5 equiv of [(η 4 -COD)RhCl] 2 and 6b combine to give [(κ 1 -P-6b)(η 4 -COD)RhCl] (7) in 79% yield. Treatment of either 2-(dimethylamino)indene (1) or 6b with a stoichiometric amount of n-BuLi, followed by the addition of 0.5 equiv of [(η 4 -COD)RhCl] 2 , produces the (η 5 -indenyl)-rhodium(I) complexes 8 (53% yield) and 9 (88% yield), respectively, in which the pnictogen donor is apparently not coordinated to the rhodium center. When 2.5 equiv of n-BuLi is combined with 6b and subsequently treated with 0.5 equiv of [(η 4 -COD)RhCl] 2 , 9 is also produced, along with a small amount of the unusual Rh 2 Li 2 species 10. The crystallographically determined structures of 2d, 3‚C 6 H 6 , 7, and 10‚C 7 H 8 are reported.
A new indene-based ligand featuring pendant phosphine sulfide and amine donor fragments has been developed; Rh(I) coordinates to the neutral form of the ligand in a kappa2-[N,S] fashion, while the anionic form of the ligand binds Rh(I) and Mn(I) in kappa2-[C,S] and eta5 modes, respectively.
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