Synthesis, Characterization and Enhanced Cleavage of Diphosphate and Triphosphate Bound to Tetraaminecobalt(III) Centers. Crystal Structure of [N,N-Bis(2-aminoethyl)ethane-1,2-diamine](diphosphato)cobalt(III) Perchlorate Monohydrate

Abstract

The complexes [Co( tren )(P₂O₇H₂)] (ClO₄).H₂O, [Co( tren )(P₃0₁₀H₃)] (ClO₄) (tren = N,N-bis(2- aminoethyl )ethane-1,2-diamine) and [Co( cyclen )(P₂O₇H₂)](ClO₄)(cyclen = 1,4,7,10-tetraazacy-clododecane ) have been prepared and characterized. The complex [Co( tren )(P₂0₇H₂)](C10₄).H₂0 crystallized in the monoclinic space group P2₁/n,a 10.655(3), b 14.675(5), c 11.260(4) Å , β 98.49(3) for a single-crystal structure determination R was 0.041 for 4043 'observed' reflections. Despite the presence of a primary and a tertiary nitrogen donor in the plane of the cobalt and the phosphate oxygen donors, bond distances to Co-N(primary) and Co-N(tertiary) at 1.926(3) and 1.924(3) Å respectively are equivalent, as are the Co-O distances of 1.940(2) and 1 .943(3) to the N(primary) and N(tertiary) respectively. Axial Co-N(primary) bonds (av. 1.952 A) are elongated compared with the in-plane N(primary), and the axial N-Co-N angle is distorted (171.6º). The hydrolysis of the diphosphate and triphosphate complexes at pH 7.3 in the presence of an assisting complex, [Co( tn )₂(OH₂)(OH)]²⁺ ( tn = propane-1,3-diamine) or [Co( tren )(OH₂)(0H)]²⁺, was followed by ³¹P n.m.r. spectroscopy, and rate enhancements of up to about 10⁴ compared with free polyphosphate were observed, with the diphosphato complexes being least sensitive to cleavage by added complex. Intermediates in which the polyphosphate bridges two metal centres are apparently involved; the inability of [Pd(en)(0H₂)₂]²⁺(en= 1,2-ethanediamine) to enhance cleavage is consistent with this, since this ion does not form complexes with polyphosphates. [Co( tren )(ATP)](ATP=adenosine triphosphate ) was also prepared but not isolated; assisted hydrolysis with [Co( tren )(OH₂)(OH)]²⁺ is about 10⁴ faster than unassisted hydrolysis of free ATP under similar conditions.