Alkoxide Attack on Coordinated Olefin Can Be Reversible

Abstract

Alkoxide (MeO -, EtO -, i PrO -) attack occurs at the coordinated olefin of Ir(Tripod)(COD) (Tripod ) MeC(CH 2 PPh 2 ) 3 , COD ) 1,5-cyclooctadiene) in CH 2 Cl 2 to give Ir(Tripod)(2-alkoxycyclooct-5-en-1-yl), primarily as the exo isomer. These products slowly eliminate alcohol to give Ir(Tripod)((1,2-η 2 )-6-σ-cycloocta-1,4-dienyl), which is the only product detected when the alkoxide is t BuO -. Addition of excess methanol to exo-Ir(Tripod)(2-methoxycyclooct-5-en-1-yl) abstracts MeO -(i.e., heterolytic O-C bond cleavage), and thus a hydrogen-bonding solvent reverses the nucleophilic attack on coordinated olefin. Alkoxide (MeO -, i PrO -, t BuOand 2-BuO -) addition occurs at an olefinic carbon of Rh(Tripod)(NBD) + (NBD ) norbornadiene) to give Rh(Tripod)(2-alkoxynorborn-4-en-1-yl). The crystal structure of the exo/ methoxy example has been determined. While this product cannot unimolecularly eliminate alcohol, attempts to protonate the norbornyl ether in the presence or absence of added NBD were not successful. Here again, acid abstracts RO -from the ligand ether.

CNH2 Bond Formation Mediated by Iridium Complexes

“…The newly formed carbocycle is 1,2-h-4-k-coordinated to iridium and functionalized with an amino fragment at the C4 sp 3 -carbon at the exo site. The coupling of the amino fragment to the apical olefin is in good agreement with the nucleophilic attack of the alkoxide group to [Ir(Tripod)(cod)] complex (Tripod = MeC(CH 2 PPh 2 ) 3 , cod = 1,5-cyclooctadiene) [18] and it has been related to the lower back donation in this position. [19] The coordination of the metal atom to the olefinic C atoms is found to be not symmetrical, with an Ir-C(2) bond (2.190(4) ) that is longer than the Ir-C(1) bond (2.092(4) ) and those found in the parent trinuclear compound (in the range of 2.098-2.142 (5) ).…”

CNH2 Bond Formation Mediated by Iridium Complexes

“…The newly formed carbocycle is 1,2‐η‐4‐κ‐coordinated to iridium and functionalized with an amino fragment at the C4 sp 3 ‐carbon at the exo site. The coupling of the amino fragment to the apical olefin is in good agreement with the nucleophilic attack of the alkoxide group to [Ir(Tripod)(cod)] complex (Tripod= MeC(CH 2 PPh 2 ) 3 , cod=1,5‐cyclooctadiene)18 and it has been related to the lower back donation in this position 19. The coordination of the metal atom to the olefinic C atoms is found to be not symmetrical, with an Ir–C(2) bond (2.190(4) Å) that is longer than the Ir–C(1) bond (2.092(4) Å) and those found in the parent trinuclear compound (in the range of 2.098–2.142(5) Å) 7a…”

Rhodium Phosphine−π-Arene Intermediates in the Hydroamination of Alkenes

“…This binding is then followed by reversible attack of the amino group on the bound alkene. Such nucleophilic attack on a bound alkene is not common for rhodium systems,49,63 but is a common reaction for cationic olefin complexes of other late transition-metal systems 64,65. Cyclization of primary amines has been more challenging to develop with late transition-metal catalysts than cyclization of secondary amines,13,14,28 and this study illustrates explicitly that the greater binding affinity of the primary amine is the likely origin of this trend.…”