Reactivity of a Cationic (C₅Me₅)Ir^III-Cyclometalated Phosphine Complex with Alkynes

Abstract

The electrophilic cationic complex [(η5-C5Me5)Ir(C∧P)]+, which contains a metalated phosphine derived from PMe(Xyl)2 (Xyl = 2,6-Me2C6H3), reacts at −60 °C with the alkynes HCCH, PhCCH, and PhCCMe, with formation of the corresponding π adducts [(η5-C5Me5)Ir(C∧P)(η2-alkyne)]+. Thermal activation of these complexes leads to products that result from the C–C coupling of the alkyne and the σ Ir–C bond of the metalated phosphine, whose nature depends markedly upon the alkyne involved. Thus, for HCCH the carbon–carbon bond -forming reaction leads to an iridium-bound alkene moiety as the thermodynamic product, whereas the analogous complexes derived from the bulkier PhCCH and PhCCMe alkynes undergo further transformation into allylic structures. Mechanistic studies supported by the use of PhCCD demonstrate the implication of an undetected vinylidene structure, IrCC(H)Ph, in the key carbon–carbon bond-forming step of the PhCCH reaction system, whereas for the internal alkyne PhCCMe a migratory insertion mechanism is operative. However, no clear distinction between these two routes can be made for the C–C bond-forming reaction for which HCCH is responsible.

Structural Mimics of Acetylene Hydratase: Tungsten Complexes Capable of Intramolecular Nucleophilic Attack on Acetylene

“…Nucleophilic attack on coordinated acetylene in an intramolecular fashion using phosphorous or carbon nucleophiles is known for transition metals, such as Mo or Ir . For example, oxidation of [Mo(C 2 H 2 )(dppe) 2 ] with [Cp 2 Fe][BF 4 ] leads to nucleophilic attack of the phosphorus on the acetylenic carbon to form the acetylene‐inserted complex [Mo(CHCH‐PPh 2 CH 2 CH 2 PPh 2 )(dppe)(MeCN) 2 ][OTf] 2 .…”

“…For example, oxidation of [Mo(C 2 H 2 )(dppe) 2 ] with [Cp 2 Fe][BF 4 ] leads to nucleophilic attack of the phosphorus on the acetylenic carbon to form the acetylene‐inserted complex [Mo(CHCH‐PPh 2 CH 2 CH 2 PPh 2 )(dppe)(MeCN) 2 ][OTf] 2 . In the complex [Ir(C 2 H 2 )( )(η 5 ‐C 5 Me 5 )][BAr F ] with the cyclometalated ligand PMe(2,6‐Me 2 C 6 H 3 ) 2 (= ) the coordinated C 2 H 2 is inserted into the σ Ir−CH 2 bond upon thermal activation . However, such reactivity has never been observed for a mononuclear W complex.…”

“…[21] In the complex [Ir(C 2 H 2 )(C _ P)(h 5 -C 5 Me 5 )][BAr F ]w ith the cyclometalated ligand PMe(2,6-Me 2 C 6 H 3 ) 2 (= C _ P) the coordinated C 2 H 2 is inserted into the s IrÀCH 2 bond upon thermala ctivation. [22] However, such reactivity has never been observed for am ononuclearWcomplex. This makes 4 and 5 the first compoundso ft heir kind, which is of particulari nterest regarding AH, because it represents the first nucleophilic attack on aW -bound C 2 H 2 and therefore supports the proposed first shell mechanism.…”

“…Nucleophilic attack on coordinated acetylene in an intramolecular fashion using phosphorous or carbonn ucleophilesi s known for transition metals, such as Mo or Ir. [21,22] For example, oxidation of [Mo(C 2 H 2 )(dppe) 2 ]w ith [Cp 2 Fe][BF 4 ]l eads to nucleophilic attack of the phosphorus on the acetylenic carbon to form the acetylene-inserted complex [Mo(CHCH-PPh 2 CH 2 CH 2 PPh 2 )(dppe)(MeCN) 2 ][OTf] 2 . [21] In the complex [Ir(C 2 H 2 )(C _ P)(h 5 -C 5 Me 5 )][BAr F ]w ith the cyclometalated ligand PMe(2,6-Me 2 C 6 H 3 ) 2 (= C _ P) the coordinated C 2 H 2 is inserted into the s IrÀCH 2 bond upon thermala ctivation.…”

Synthesis, Structures, and Reactivity of Single and Double Cyclometalated Complexes Formed by Reactions of [Cp*MCl2]2 (M = Ir and Rh) with Dinaphthyl Phosphines

“…Recently, some alkyne insertion reactions of five-membered cycloiridated complexes were studied in the presence of NaBAr F 4 , which presented 1,2-insertion mode or 1,1-insertion mode after the initial vinylidene rearrangement. 30 Thus, we have further investigated the reactivity of 3b with terminal aryl acetylenes and NaBAr F 4 . When a mixture of 3b with p -RC 6 H 4 C≡CH (R = H, MeO, or F) and NaBAr F 4 in CH 2 Cl 2 was stirred at room temperature for 30 min, a yellow-green crystal was obtained by recrystallization.…”