Easily Prepared Chiral Scorpionates: Tris(2-oxazolinyl)boratoiridium(I) Compounds and Their Interactions with MeOTf

Abstract

Optically active C 3 -symmetric monoanionic ligands are uncommon in organometallic chemistry. Here we describe the synthesis of readily prepared tris(4S-isopropyl-2-oxazolinyl)phenylborate [To P ] and fluxional, zwitterionic four-and five-coordinate iridium(I) compounds [Ir(To P )-(η 4 -C 8 H 12 )] ( 4) and [Ir(To P )(CO) 2 ] (5). The highly fluxional nature of 4 and 5 makes structural assignment difficult, and the interaction between the iridium(I) center and the [To P ] ligand is established by solid-state and solution 15 N NMR methods that permit the direct comparison between solution and solid-state structures. Although iridium cyclooctadiene 4 is a mixture of four-and five-coordinate species, the dicarbonyl 5 is only the five-coordinate isomer. The addition of electrophiles MeOTf and MeI provides the oxazoline N-methylated product rather than the iridium methyl oxidative addition product. N-Methylation was unequivocally proven by through-bond coupling observed in 1 H-15 N HMBC experiments.

Optically active, bulky tris(oxazolinyl)borato magnesium and calcium compounds for asymmetric hydroamination/cyclization

“…The IR spectrum of LiOx tBu (KBr) contained n CN bands due to both isocyanide (2000 cm À1 ) and oxazolide (1635 cm À1 ), and this is consistent with previous observations with 4,4-dimethyl-2-lithiooxazolide and 4S-isopropyl-2-lithio-oxazolide [16,19].…”

“…We also prepared a chiral analog from the readily-available, L-valine-derived 4S-isopropyl-2-oxazoline to provide tris(4S-isopropyl-2-oxazolinyl)phenylborate [To P ] À [16]. In contrast to the synthesis of [To M ] À , deprotonation of 2H-4S-isopropyl-2-oxazoline with nBuLi proceeds in lower yield (ca.…”

Synthesis and Oxidation Catalysis of [Tris(oxazolinyl)borato]cobalt(II) Scorpionates

“…In particular, the electron‐donating properties and bowl‐like steric environment provided by the coordination pocket of To M could stabilize reactive groups bonded to metal centers with accessible d electrons to facilitate catalytic chemistry. Moreover, a series of optically active tris(4‐R‐2‐oxazolinyl)phenylborate ligands are also available for imposing chiral environments on tetrahedrally coordinated first‐row transition‐metal sites …”

Hydroelementation of Unsaturated C–C Bonds Catalyzed by Metal Scorpionate Complexes

“…Tris(pyrazole)methane substitutes the anionic central borate atom for a neutral carbon atom, generating neutral analogues. The donor atom is typically nitrogen, including, but not limited to, imidazole, oxazole, and triazole rings, although the field has grown to include imidazole‐2‐thione and 3‐mercapto‐1,2,4‐triazole rings bearing a sulfur donor atom, and tripodal phosphine ligands, a field unto itself.…”