A Significant but Constrained Geometry Pt→Al Interaction: Fixation of CO₂ and CS₂, Activation of H₂ and PhCONH₂

Abstract

Reaction of the geminal PAl ligand [Mes2PC(═CHPh)AltBu2] (1) with [Pt(PPh3)2(ethylene)] affords the T-shape Pt complex [(1)Pt(PPh3)] (2). X-ray diffraction analysis and DFT calculations reveal the presence of a significant Pt→Al interaction in 2, despite the strain associated with the four-membered cyclic structure. The Pt···Al distance is short [2.561(1) Å], the Al center is in a pyramidal environment [Σ(C-Al-C) = 346.6°], and the PCAl framework is strongly bent (98.3°). Release of the ring strain and formation of X→Al interactions (X = O, S, H) impart rich reactivity. Complex 2 reacts with CO2 to give the T-shape adduct 3 stabilized by an O→Al interaction, which is a rare example of a CO2 adduct of a group 10 metal and actually the first with η(1)-CO2 coordination. Reaction of 2 with CS2 affords the crystalline complex 4, in which the PPtP framework is bent, the CS2 molecule is η(2)-coordinated to Pt, and one S atom interacts with Al. The Pt complex 2 also smoothly reacts with H2 and benzamide PhCONH2 via oxidative addition of H-H and H-N bonds, respectively. The ensuing complexes 5 and 7 are stabilized by Pt-H→Al and Pt-NH-C(Ph) = O→Al bridging interactions, resulting in 5- and 7-membered metallacycles, respectively. DFT calculations have been performed in parallel with the experimental work. In particular, the mechanism of reaction of 2 with H2 has been thoroughly analyzed, and the role of the Lewis acid moiety has been delineated. These results generalize the concept of constrained geometry TM→LA interactions and demonstrate the ability of Al-based ambiphilic ligands to participate in TM/LA cooperative reactivity. They extend the scope of small molecule substrates prone to such cooperative activation and contribute to improve our knowledge of the underlying factors.

Lewis Acid Transition‐Metal‐Catalyzed Hydrogen Activation: Structures, Mechanisms, and Reactivities

“…Along the dissociative mechanism, it is only uphill by 14.3 kcal mol −1 in free energy for the dissociation of the Pt→B bond and the insertion of the H 2 molecule (from D ‐RC to D ‐IM ). A similar feasible Pt→Al dissociation was also proposed in Bourissou's analogous AlIM‐Pt system . In D ‐IM , H 2 is activated by the σ(H 2 )→p(B) dative interaction and the d(Pt)→σ*(H 2 ) back‐donation interaction.…”

Synthesis and Electronic Characterization of Iridium‐Aluminum and Rhodium‐Aluminum Heterobimetallic Complexes Bridged by 3‐Oxypyridine and 4‐Oxypyridine

“…The majority of known, well‐characterized late transition metal‐aluminum heterobimetallic complexes have been obtained by first synthesizing an aluminum‐based ligand and subsequently introducing it to an appropriate transition metal precursor , , . In contrast, our lab has had recent success crafting late transition metal‐aluminum heterobimetallics by first synthesizing transition metal complexes containing a substituent to which aluminum could bind, and subsequently reacting it with an appropriate aluminum precursor , .…”

“…In contrast, our interest lies primarily in pairing aluminum with an electron rich, late transition metal with the goal of exploiting synergistic acid/base behavior between the two metal sites. The late transition metal‐aluminum bonding motif has been found to be quite useful for both stoichiometric and catalytic bond activations , , , , …”

Oxidative‐Insertion Reactivity Across a Geometrically Constrained Metal→Borane Interaction

“…Notably,t hese heteroallene C = O bond oxidative insertions into the Pt!Bb ond in 1 can be compared to the insertion of CO 2 into aplatinum!alane unit recently reported by Bourissou and co-workers.Inthis latter Figure 2. [46] Putative unobserved intermediates (C)r esulting from insertion of CO 2 or tBuNCO with 1.P utative unobserved intermediate( D)resulting from oxidativei nsertion of MeCN with 1. [51] Scheme 3.…”

“…[46] While reaction of 1 with O = C = E (E = O, NtBu) is believed to proceed analogously through an intermediate heteroallene adduct (C;Scheme 3), [47] cyclohexyl group migration within the Cy2 BIM framework produces an X-type amido ligand bound to aLewis-acidic Pt center, rather than retention of an eutral L-type donor ligand. [46] While reaction of 1 with O = C = E (E = O, NtBu) is believed to proceed analogously through an intermediate heteroallene adduct (C;Scheme 3), [47] cyclohexyl group migration within the Cy2 BIM framework produces an X-type amido ligand bound to aLewis-acidic Pt center, rather than retention of an eutral L-type donor ligand.…”