Synthesis and Characterization of Magnesium and Aluminum Bis(phosphoranyl)methanediide Complexes

Abstract

The reaction of [CH 2 (PPh 2 dNSiMe 3 )(PPh 2 dE)] (E = S (1), NSiMe 3 (2)) with Mg(Bu n ) 2 in refluxing toluene afforded the magnesium bis(phosphoranyl)methanediide complexes [{(PPh 2 dNSiMe 3 )-(PPh 2 dE)}CMg] 2 (E = S (3), NSiMe 3 (4)), respectively. The X-ray structures and DFT calculations of 3 and 4 show that they are bimetallic methanediide complexes of magnesium containing a strong Mg-C methanediide electrostatic bonding. Treatment of 4 with water in toluene gave 2 and the magnesium hydroxide complex [HC(PPh 2 dNSiMe 3 ) 2 Mg(μ-OH)] 2 (5), confirmed by X-ray crystallography. The reaction of 1 with AlMe 3 in refluxing toluene afforded the aluminum bis(phosphoranyl)methanediide complex [{(PPh 2 dNSiMe 3 )(PPh 2 dS)}CAlMe] 2 (6). The X-ray structure of 6 shows that a methanediide carbon is bonded to one aluminum atom. DFT calculations of 6 demonstrate that Al-C methanediide is highly polar with weak covalent bonding, consistent with the topological analysis of electron densities of 6.

Methanediide Formation via Hydrogen Elimination in Magnesium versus Aluminium Hydride Complexes of a Sterically Demanding Bis(iminophosphoranyl)methanediide

“…2.38-2.47 Å) contact each, whereas all Mg-C distances are of the short type in Example B (M = Mg, E = NSiMe 3 : ca. 2.20-2.25 Å) [16]. Thus, the Mg-C coordination approaches the extreme case that was previously found for [L(AlX 2 ) 2 ] [33].…”

“…In these compounds, the Mg centre(s) could show an environment with a relatively low coordination number and the close proximity of the formally dianionic carbon centre of the methanediide and the dicationic Mg 2+ centre could allow for some interesting activation chemistry of small molecules. Secondly, the Mg•••Mg separation in the known Mg complexes of structure type B (e.g., 2.87 Å for E = NSiMe3) [16] shows a distance similar to those in dimeric magnesium(I) complexes with unsupported Mg-Mg bonds [25,26]. Thus, a stable dimeric complex may possibly serve as a starting material to a molecule with a supported Mg-Mg bond.…”

“…For the respective complex with R = Me and Ar = Dip [29] In analogy to the synthesis of a sterically less hindered methanediide Mg complex of type B (M = Mg, E = NSiMe3) [16], which was synthesized at 140 °C using MgnBu2, we heated [HLMgnBu] 1 to various high temperatures (up to 200 °C) though only obtained a complex product mixture were found for R = Me and Ar = 2,6-(Ph2CH)2-4-MeC6H2 (≡ Ar*) [27], and R = tBu and Ar = Dip [28]. For the respective complex with R = Me and Ar = Dip [29] In analogy to the synthesis of a sterically less hindered methanediide Mg complex of type B (M = Mg, E = NSiMe3) [16], which was synthesized at 140 °C using MgnBu2, we heated [HLMgnBu] 1 to various high temperatures (up to 200 °C) though only obtained a complex product mixture In analogy to the synthesis of a sterically less hindered methanediide Mg complex of type B (M = Mg, E = NSiMe 3 ) [16], which was synthesized at 140 • C using MgnBu 2 [27,[30][31][32]. No reaction was observed between 1 and one equivalent of PhSiH 3 at room temperature; however, at elevated temperatures, for example in toluene at 80 • C, this afforded colourless crystals of the new homoleptic methanediide complex [(LMg) 2 ] 2 in moderate isolated yield, see Scheme 1 and Figure 3.…”

“…Methanediides show several bonding modes containing typically one or two coordinated metal centres [2][3][4][5][6][7][8]. Over the past years, several examples of alkaline earth metal complexes of substituted bis(phosphoranyl)methanides and -methanediides have been forthcoming [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] that show several coordination types B-E, see Figure 1. Most common is a dimeric Most common is a dimeric structure (B) with central M2C2 four-membered ring and additional M-E coordination, and monomeric complexes (C) with an N,C,N′-chelating methanide ligand and additional donors coordinating to the metal centre.…”

{CH2(PPh2=NSiMe3)(PPh2=S)} and {CH(PPh2=NSiMe3)(Ph2P=S)}– as Ligands in Zinc Chemistry: Synthesis and Structures

“…The synthesis of {CH 2 (PPh 2 =NSiMe 3 )(PPh 2 =S)} by the reaction of {Ph 2 PCH 2 (PPh 2 =NSiMe 3 )} with sulfur in toluene at reflux was reported by So and co-workers. [42] [43] Al, [43] Sn, [44,45] Ru, [46] Pt, [47] and the rare-earth elements [48] Single crystals of compounds 1 and 2 were obtained from hot THF directly from the reaction mixture. Compound 1 crystallizes in the monoclinic space group Cc with two independent molecules of 1 in the asymmetric unit ( Figure 1).…”