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Magnesium(I) Dimers Bearing Tripodal Diimine–Enolate Ligands: Proficient Reagents for the Controlled Reductive Activation of CO 2 and SO 2
Author(s) -
Boutland Aaron J.,
Pernik Indrek,
Stasch Andreas,
Jones Cameron
Publication year - 2015
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201502755
Subject(s) - diimine , reagent , bearing (navigation) , chemistry , magnesium , reductive elimination , medicinal chemistry , stereochemistry , combinatorial chemistry , organic chemistry , catalysis , physics , astronomy
The first examples of magnesium(I) dimers bearing tripodal ligands, [(Mg{κ 3 ‐ N , N ′, O ‐(ArNCMe) 2 (OCCPh 2 )CH}) 2 ] [Ar=2,6‐ i Pr 2 C 6 H 3 (Dip) 7 , 2,6‐Et 2 C 6 H 3 (Dep) 8 , or mesityl (Mes) 9 ] have been prepared by post‐synthetic modification of the β‐diketiminato ligands of previously reported magnesium(I) systems, using diphenylketene, OCCPh 2 . In contrast, related reactions between β‐diketiminato magnesium(I) dimers and the isoelectronic ketenimine, MesNCCPh 2 , resulted in reductive insertion of the substrate into the MgMg bond of the magnesium(I) reactant, and formation of [{(Nacnac)Mg} 2 {μ‐κ 2 ‐ N , C ‐(Mes)NCCPh 2 }] (Nacnac=[(ArNCMe) 2 CH] − ; Ar=Dep 10 or Mes 11 ). Reactions of the four‐coordinate magnesium(I) dimer 8 with excess CO 2 are readily controlled, and cleanly give carbonate [(LMg) 2 (μ‐κ 2 :κ 2 ‐CO 3 )] 12 (L=[κ 3 ‐ N , N ′, O ‐(DepNCMe) 2 (OCCPh 2 )CH] − ; thermodynamic product), or oxalate [(LMg) 2 (μ‐κ 2 :κ 2 ‐C 2 O 4 )] 13 (kinetic product), depending on the reaction temperature. Compound 12 and CO are formed by reductive disproportionation of CO 2 , whereas 13 results from reductive coupling of two molecules of the gas. Treatment of 8 with an excess of N 2 O cleanly gives the μ‐oxo complex [(LMg) 2 (μ‐O)] 14 , which reacts facilely with CO 2 to give 12 . This result presents the possibility that 14 is an intermediate in the formation of 12 from the reaction of 8 and CO 2 . In contrast to its reactions with CO 2 , 8 reacts with SO 2 over a wide temperature range to give only one product; the first example of a magnesium dithionite complex, [(LMg) 2 (μ‐κ 2 :κ 2 ‐S 2 O 4 )] 16 , which is formed by reductive coupling of two molecules of SO 2 , and is closely related to f‐block metal dithionite complexes derived from similar SO 2 reductive coupling processes. On the whole, this study strengthens previously proposed analogies between the reactivities of magnesium(I) systems and low‐valent f‐block metal complexes, especially with respect to small molecule activations.