Synthesis of the (Dialkylamino)borate, [Ph₂B(CH₂NMe₂)₂]^-, Affords Access to N-Chelated Rhodium(I) Zwitterions

Abstract

This paper reports the synthesis of the first bis(amino)borate ligand, [Ph 2 B(CH 2 NMe 2 ) 2 ] -, an anionic equivalent of tertiary diamines. Anionic [Ph 2 B(CH 2 NMe 2 ) 2 ] is an excellent bidentate ligand auxiliary and is used to prepare a series of N-chelated, zwitterionic rhodium-(I) complexes.

Zwitterionic Relatives of Cationic Platinum Group Metal Complexes: Applications in Stoichiometric and Catalytic σ‐Bond Activation

“…[93,94] In keeping with previously characterized PGM zwitterions of this type, crystallographic data obtained for 46-48 and 51 revealed no inter-or intramolecular ion-pairing interactions, Scheme 14. Cationic and zwitterionic platinum complexes, including benzene CÀH bond activation by the platinum zwitterion 32, leading to 34. and the observed Rh···B distances (> 3.6 ) confirmed that the borate fragment is spatially separated from the rhodium center.…”

Zwitterionic Relatives to the Classic [(P–P)Rh(solv)2]+ Ions: Neutral Catalysts Active for HE Bond Additions to Olefins (E=C, Si, B)

“…[5] The rhodium(i) zwitterions introduced herein ( Figure 1) feature a borate counteranion that is fastened within the ligand backbone and partially insulated from the coordinated metal center by tertiary phosphanes and amines. [6,7] These complexes are distinct from previously prepared bis(pyrazolyl)borate rhodium complexes, [8] where resonance delocalization of the borate charge is likely to be more prevalent.…”

“…No inter-or intramolecular ion-pairing interactions are observed, consistent with the amine-chelated zwitterion that was characterized previously. [7] The [Ph 2 B(CH 2 PPh 2 ) 2 ] À ligand conformation for dicarbonyl 11 is distinct from its conformation in the other three structures and places the borate unit slightly closer (% 0.1 ) to the bound rhodium center (RhÀB 3.908(3) in 11). One possible explanation for this ligand distortion is that the borate unit is drawn closer to the metal center to compensate for the increased electrophilicity at the rhodium center because of the strongly p-acidic carbonyl ligands.…”

“…The synthetic details for the amine-chelated complexes were recently communicated elsewhere. [7] Briefly, zwitterionic phosphane precatalysts were prepared in high yield by reaction of the diene-rhodium precursors [{(nbd) (10), were derived in a similar fashion from norbornadiene precursors that were previously reported. [11, 4a] Owing to their novelty, it was of interest to briefly canvass the structural characteristics and substitution chemistry of the phosphane- The solid-state structures of complexes 1 a, 2, 11, and 14 were determined by X-ray diffraction studies.…”

“…[13] A similar trend has been observed for the amine-based systems. [7] The increased electron-richness of the zwitterions in comparison to their corresponding cations might be expected to attenuate or shut down their ability to mediate catalytic transformations, especially those reactions typical of electrophilic [(P-P)Rh(solv) 2 ] + complexes. Our data, however, suggests otherwise.…”