Process for preparation of diphosphine compounds and intermediates for the process

1. A production method of a phosphine-borane complex represented by the formula

wherein R 3′ , R 5′ , R 6′ and R 8′ are each a hydrogen atom, a lower alkyl group or a lower alkoxy group, R 4′ and R 7′ are each a fluorine atom, a chlorine atom, a tert-butyl group, a mono-lower alkylamino group or a di-lower alkylamino group, and R 9′ and R 10′ are each a hydrogen atom or a lower alkyl group (R 3′ and R 4′ , and R 7′ and R 8′ may form a lower alkylenedioxy group) (provided that R 3′ , R 4′ , R 5′ , R 6′ , R 7′ , R 8′ , R 9′ and R 10′ are not hydrogen atoms at the same time), or a salt thereof, which comprises reducing a compound represented by the formula

wherein each symbol is as defined above, or a salt thereof, with lithium aluminum hydride in the presence of cerium chloride and sodium borohydride.

2. A phosphine-borane complex represented by the formula

wherein R 3′ , R 5′ , R 6′ and R 8′ are each a hydrogen atom, a lower alkyl group or a lower alkoxy group, and R 4′ and R 7′ are each a fluorine atom, a chlorine atom, a tert-butyl group, a mono-lower alkylamino group or a di-lower alkylamino group (R 3′ and R 4′ , and R 7′ and R 8′ may each form a lower alkylenedioxy group) (provided that a compound wherein R 5′ and R 6′ are hydrogen atoms, and R 3′ and R 4′ , and R 7′ and R 8′ form a methyldioxy group is excluded), or a salt thereof.