Self-Isomerized–Cyclometalated Rhodium NHC Complexes as Active Catalysts in the Hydrosilylation of Internal Alkynes

• DOI: 10.1021/acs.organomet.1c00409
• Publication Date: 2022-01-24T17:32:05Z
• Authors: Estefan van Vuuren; Frederick P. Malan; Werner Cordier; Margo Nell; Marilé Landman
• Keywords: Hydrosilylation

A range of unique Rh-based bidentate NHC complexes that are formed in a base-free tandem isomerization/cyclometalation process were synthesized (1–4) from imidazolium salts with an N-alkenyl tether. Cyclometalation occurred complex 1, leading to unprecedented complex, which is the first and only example literature nonaromatic C(sp2)–H activation C(sp3)–Rh cyclometalated product concomitant intramolecular/isomerization process. Dealkylation substituent form byproducts showed metal N-coordination (1b 2b). These byproducts, 1b 2b, further reacted anion exchange reagent NH4PF6 dimeric 1bd 2bd. All applied as precatalysts hydrosilylation internal alkynes excellent performance (conversions 66–100%) after 1 h at 80 °C without use additive. Anticancer studies presented half-maximum inhibitory concentrations ranging 3.71 25.85 μM. Depending on cell line, 4 was most cytotoxic especially BT-20 triple-negative breast carcinoma, MCF-12A nontumorigenic mammary gland cell, MDA-MB-231 MCF-7/TAMR-1 tamoxifen-resistant subtype MCF-7 estrogen- progesterone-positive luminal carcinoma lines.