A fluorenyl-tethered N-heterocyclic carbene LH (LH = [(Flu)HÀ (CH 2 ) 2 À NHC Dipp ]) and its monoanionic version L À are explored in complexation with zinc towards the hydroboration of N-heteroarenes, carbonyl, ester, amide, and nitrile under ambient condition. The N-heteroarenes exhibit high 1,2-regioselectivity which is justified by computational analyses. The relative hydroboration rates of differently p-substituted (electron donating vs. withdrawing) pyridines are also addressed. The monodentate LH offers a better catalytic activity than the chelating L À for steric reasons despite both giving three-coordinate zinc complexes. The mechanism involves a ZnÀ H species at the heart of these catalytic processes which is trapped by Ph 2 CO. Computational studies suggest that the barrier to form the hydride complex is comparable to the barrier required for the following hydride transfer to pyridine.

Archetypal metalloenzyme Cytochrome P450cam (CYP101A1) catalyzes regioselective hydroxylation of its native substrate camphor in heme active site. However, the proposal of potential existence of additional substrate binding modes distal from the active site in P450cam and their concomitant roles in regulating recognition at active site have remained a matter of recurring discourse. Herein we report the discovery of a novel3sitestate in P450cam, where three substrate molecules were observed to simultaneously bind to P450cam at three distinct sites including the heme active site. These three binding modes, hereby referred ascatalytic,waitingandallostericbinding modes in3sitestate, are allosterically inter-linked and function in mutually synergistic fashion. The3sitestate possesses regio-selective conformations of substrate essential for catalysis and establishes substrate-ingress and product exit process to and from the active site via two distinct channels. The ensemble of three-state binding modes are found to be self-consistent with NMR pseudo-contact shift data obtained from TROSY-HSQC measurements and DEER based predictions. Binding of redox partner Putidaredoxin with3sitemodel retains closed conformation of 3site state, siding with NMR based hypothesis that the catalysis would take place in closed insulation of P450cam even in presence of its redox partner.