Reactivity of Unsupported Transition Metal-Aluminyl Complexes: A Nucleophilic TM-Al Bond

Abstract

Despite the long history of research in transition metal (TM) complexes, the study of TM-aluminyl complexes is still in its early stage of development. It is expected that the presence of an electropositive Al donor atom would open up new possibilities in TM complex reactivity, and indeed TM-aluminyl has shown an early sign of success in small-molecule activation. On the other hand, the existing reports on TM-aluminyl reactivity are often explained to readers with different understanding on individual cases, and a general picture of TM-aluminyl reactivity is still not available. In this work, we have attempted to provide a systematic picture to explain some early explorations in this field, specifically a series of recently reported heteroallene insertion reactions involving unsupported TM-aluminyl complexes. Through density functional theory calculations of a number of TM-aluminyl complexes, covering both Au and Cu centers, we found that their reactivity against heteroallenes (including CO 2 and carbodiimides) is mostly based on the strong nucleophilicity of the TM−Al σ-bond.

Inducing Nucleophilic Reactivity at Beryllium with an Aluminyl Ligand

“…This connectivity is consistent with nucleophilic attack by beryllium at the electrophilic carbon center of the carbodiimide, while the aluminium center acts as the electrophilic site, which results in Al–N bond formation. Although steric factors may influence the product formed in this reaction, the result is in line with the calculated charge distribution within 3 . The nucleophilic reactivity of s-block metals is extremely rare, and previously unknown for beryllium …”

“…Although steric factors may influence the product formed in this reaction, the result is in line with the calculated charge distribution within 3. 27 The nucleophilic reactivity of s-block metals is extremely rare, and previously unknown for beryllium. 19 The reactivity of 4�for which the polarity of the M−M bond is calculated to be inverted compared with 3�with N,N′-diisopropylcarbodiimide was also examined (Scheme 2, left).…”

Cooperation towards nobility: equipping first-row transition metals with an aluminium sword

“…Decomposition of species 149 results in oxo-bridged species 150 , which reacts with another molecule of CO 2 to eventually furnish carbonate-bridged species 151 . Further computational studies by Lin, Sheong and co-workers 205 concluded that the rate-determining insertion of CO 2 and carbodiimide is followed by several rearrangements, supporting McMullin and Hill's work. The insertion, however, is proposed to be initiated by the nucleophilic attack of the σ-(Cu–Al) bond on the heteroallene coupling partner, providing valuable insight for developing future Cu–Al-mediated reactivity.…”

The emerging chemistry of the aluminyl anion

“…In this respect, the reactions of the coinage metal complexes with CO 2 have been studied experimentally and using computational methods. 53 Initial reports on the reaction of the Al–Au system 42 with CO 2 identified the product as the dioxocarbene ( xanth NON)Al(O 2 C)Au(P t Bu 3 ) 50 (Type- B ), with crystallographic analysis confirming a μ-1κ 2 O , O ′:2κ C -bonding mode for the CO 2 -unit formed by the reductive insertion of CO 2 into the Al–Au bond. 50 This result has since been obtained with other Al– M compounds, affording the related dioxocarbenes for M = Cu: (NC 2 N Dipp )Al(O 2 C)Cu(P t Bu 3 ) 51 , (NC 2 N Dipp )Al(O 2 C)Cu(NHC iPr ) 52 , (NC 2 N Dipp )Al(O 2 C)Cu( Me2 CAAC) 53 ; M = Ag: ( xanth NON)Al(O 2 C)Ag(P t Bu 3 ) 54 , (NC 2 N Dipp )Al(O 2 C)Ag(NHC iPr ) 55 ; M = Au: (NC 2 N Dipp )Al(O 2 C)Au(NHC iPr ) 56 .…”