Iron(ii) catalysts containing diimino-diphosphine tetradentate ligands and their synthesis

A hydrogenation catalyst comprising a hexa-coordinate iron(II) complex of formula (I)

• wherein a trans coordination geometry is achieved at iron through nitrogen and phosphorus donor bonds of a tetradentate diimino-diphosphine templated ligand of the formula (II):
• R12P-A-C(R4)═N—C*(R5R6)—C*(R7R8)—N═C(R4)-A-PR12 (II)
• and L1 and L2 are in an axial coordination above and below the templated ligand, respectively,
• wherein the tetradentate diimino-diphosphine templated ligand is the reaction product of a phosphinaldehyde precursor of formula (V)
• and a diamine precursor of formula (VI)
• wherein
• each R1 is independently selected from the group consisting of aryl, heteroaryl, C1-C8 alkyl, C2-C8 alkenyl, C1-C8 alkoxy, aryloxy, and cycloalkyl, all of which may be optionally substituted;
• two geminal R1 groups may combine to form a C2-C4 linear alkyl diradical or C3-C8 branched alkyl diradical, each of which may be optionally substituted, to form a ring together with the phosphorus atom to which they are attached;
• or two R1 groups, each of which is located on a different phosphorus atom, may combine to form a linker M, wherein M is selected from the group consisting of C2-C4 linear alkyl diradical and C3-C8 branched alkyl diradical, each of which may be optionally substituted, or M may be a diradical ligand with a wide bite angle;
• A is
• wherein each R2 and R3 are independently selected from the group consisting of H, substituted or unsubstituted C1-C8 alkyl, substituted or unsubstituted C2-C8 alkenyl, substituted or unsubstituted aryl, and substituted or unsubstituted cycloalkyl, and each n is an integer independently selected from 1, 2, and 3;
• each R4 is independently selected from the group consisting of H, substituted or unsubstituted C1-C8 alkyl, substituted or unsubstituted C2-C8 alkenyl, substituted or unsubstituted aryl, and substituted or unsubstituted cycloalkyl;
• each R5, R6, R7 and R8 is independently selected from the group consisting of H, substituted or unsubstituted C1-C8 alkyl, substituted or unsubstituted C2-C8 alkenyl, substituted or unsubstituted aryl, and substituted or unsubstituted cycloalkyl;
• R5 and R6, together with the carbon atom to which they are attached, may combine to form a substituted or unsubstituted cycloalkyl ring of size from 5-8 carbons;
• R7 and R8, together with the carbon atom to which they are attached, may combine to form a substituted or unsubstituted cycloalkyl ring of size from 5-8 carbons;
• or R5, R6, R7 and R8, together with the carbon atoms to which they are attached, may combine to form a group selected from
• each of which may be optionally substituted with one or more substituents selected from the group consisting of C1-C8 alkyl, C1-C8 alkoxy, and halogen atoms;
• L1 and L2 are independently selected from the group consisting of CO;
• hydride;
• pyridine and derivatives thereof;
• imidazole and derivatives thereof;
• halide ion;
• NCR, CNR and −OR, wherein R is independently selected from the group consisting of aryl, heteroaryl, C1-C8 alkyl, C2-C8 alkenyl and cycloalkyl, all of which may be optionally substituted;
• RaRbRcN wherein Ra, Rb, and Rc are independently selected from the group consisting of H and C1-C2 alkyl;
• and Rc(CO)Rd wherein Rc and Rd are independently selected from the group consisting of C1-C8 alkyl, aryl, and heteroaryl;
• m represents the charge of the compound of formula (I) and is 0, +1, or +2;
• and when m is +1 or +2, the iron (II) complex comprises at least one counter ion to counterbalance the charge of the compound of formula (I);
• with the proviso that when A is
• then at least one of L1 and L2 must be selected from the group consisting of CO and CNR, wherein R is as defined above.

A process for preparing a phosphonium dimer of formula (XIII) is provided:

• wherein R1 is selected from the group consisting of C1-C8 alkyl, C1-C8 substituted alkyl, cycloalkyl, and substituted cycloalkyl, and X is selected from the group consisting of Br and I, the process comprising:
• reacting a compound of formula (XI):
• HPR12 (XI)
• wherein R1 is as defined above;
• with a compound of formula (XII):
• wherein X is as defined above, and Re is C1-C8 alkyl, or the two Re can combine to form a C2-C3 linear alkyl diradical;
• and heating the reaction product in the presence of water to form the phosphonium dimer of formula (XIII).