Embedding a Ruthenium-Based Structural Mimic of the [Fe]-Hydrogenase Cofactor into Papain

Abstract

We describe the synthesis of the ruthenacyclic carbamoyl complexes [Ru(2-NHC(O)CHNMe)(CO)( o,o-Me-CHS)(L)] (L = HO or MeCN), which have a labile water or acetonitrile ligand at their sixth coordination sites. Steric bulk around the ruthenium center is essential in preventing isomerization and dimerization, and embedding within papain can be achieved via coordination of its sole free cysteine residue. The observed chemistry parallels that of the natural [Fe]-hydrogenase.

Very strong trans effect in ruthenacyclic carbamoyl complexes leads to ligand redistribution in phosphine derivatives

“…As indicated above, the transient species B has been observed for both 3a and 3b; its IR spectrum is red shifted from that of 3a and 3b, and there is no corresponding resonance in the 31 P NMR spectrum, suggesting that it does not contain a phosphine ligand. We have tentatively assigned it to a dimeric species with two bridging bromide ligands, viz., [Ru(µ-Br)(2-NHC(O)C5H4N)(CO)2]2, which may be thought of as having been formed through A; the red-shift in the IR values are consistent with that reported earlier for the dimeric compound [Ru(2-NHC(O)C5H4N)(SC6H4Me)(CO)2]2 [26]. Similarly, the transient species C observed for 3b" may be assigned to a dimer of A", viz., [Ru(µ-2-S-C5H4N)(2-NHC(O)C5H4N)(CO)2]2, bridged by two sulphur atoms of the mercaptopyridine ligand; this is similar to that reported for the iron analogue [Fe(µ-2-S-C5H3N-6-Me)(COMe)2(CO)2]2 [10].…”

“…Adding one equivalent of the phosphine to 3a gives 4a only (Figure S6). Similar observations are made with PMe3, which gives 3b and then 4b, and the chloro analogue 1' which gives 4a' with PPh3; complex 1' also exists as a mixture of two isomers (from its IR spectrum) [26]. Scheme 1.…”

“…The ruthenacyclic carbamoyl complex 1, which exists as an ~1:1 mixture of two isomers in solution [26], undergoes rapid substitution of the acetonitrile ligand with triphenylphosphine at ambient temperature to afford the monosubstituted product 3a. The latter undergoes a redistribution of the phosphine ligand in solution, slowly, to re-form 1 and the disubstituted derivative 4a (Scheme 1).…”

“…A large variety of ironbased model complexes for the metal cofactor have been reported [8][9][10][11][12][13][14][15][16][17][18], including some which mimic the function of the natural enzyme [19][20][21][22]. Since ruthenium complexes are known to catalyse a wide variety of reactions that utilise or involve hydrogen or hydrogenation [23][24][25], we thought that it made sense to also examine ruthenium-based structural mimics such as 1 and 2 (Figure 1b), which we have reported earlier [26][27][28]. In what appeared to be a straightforward study, we looked at the reactivity of the complexes 1/1' and 2 with phosphine ligands as a general assessment of their chemical reactivity.…”

Group VIII carbamoyl complexes as catalysts for alkyne hydrocarboxylation and electrochemical proton reduction

“…8,9,10,11 We recently reported the synthesis and physical properties of metallacyclic carbamoyl complexes 1n as structural analogues of this cofactor for the group VIII triad, viz., iron, ruthenium and osmium (Figure 1b). 12,13,14 An interesting aspect of these complexes is that the 2mercaptopyridine ligand is hemilabile; it imparts stability to the complexes and yet is capable of decoordination at the pyridine-N. 12 This property makes the complexes potential catalysts and indeed, as we would like to report here, they are efficient catalysts for alkyne hydroxycarboxylation and electrochemical proton reduction.…”