Crystal structure of NiFe(CO)₅[tris(pyridyl-meth-yl)aza-phosphatrane]: a synthetic mimic of the NiFe hydrogenase active site incorporating a pendant pyridine base.

ABSTRACT: The reaction of Ni(TPAP)(COD) {where TPAP = [(NC₅H₄)CH₂]₃P(NC₂H₄)₃N} with Fe(CO)₅ resulted in the isolation of the title heterobimetallic NiFe(TPAP)(CO)₅ complex di-?-carbonyl-tricarbon-yl[2,8,9-tris-(pyridin-2-yl-meth-yl)-2,5,8,9-tetra-aza-1-phosphabi-cyclo-[3.3.3]undeca-ne]ironnickel, [FeNi(C₂₄H₃₀N₇P)(CO)₅]. Characterization of the complex by ¹H and ³¹P NMR as well as IR spectroscopy are presented. The structure of NiFe(TPAP)(CO)₅ reveals three terminally bound CO mol-ecules on Fe⁰, two bridging CO mol-ecules between Ni⁰ and Fe⁰, and TPAP coordinated to Ni⁰. The Ni-Fe bond length is 2.4828?(4)?Å, similar to that of the reduced form of the active site of NiFe hydrogenase (?2.5?Å). Additionally, a proximal pendant base from one of the non-coordinating pyridine groups of TPAP is also present. Although involvement of a pendant base has been cited in the mechanism of NiFe hydrogenase, this moiety has yet to be incorporated in a structurally characterized synthetic mimic with key structural motifs (terminally bound CO or CN ligands on Fe). Thus, the title complex NiFe(TPAP)(CO)₅ is an unique synthetic model for NiFe hydrogenase. In the crystal, the complex mol-ecules are linked by C-H?O hydrogen bonds, forming undulating layers parallel to (100). Within the layers, there are offset ?-? [inter-centroid distance = 3.2739?(5)?Å] and C-H?? inter-actions present. The layers are linked by further C-H?? inter-actions, forming a supra-molecular framework.

SUBMITTER: Sutthirat N 

PROVIDER: S-EPMC6509684 | biostudies-literature | 2019 Apr

REPOSITORIES: biostudies-literature