Heavier alkaline earth metal complexes with phosphinoselenoic amides: evidence of direct M–Se contact (M = Ca, Sr, Ba)

Abstract

We report here a series of heavier alkaline earth metal complexes with a phosphinoselenoic amide ligand using two synthetic routes. In the first route, the heavier alkaline earth metal bis(trimethylsilyl)amides [M{N(SiMe3)2}2(THF)n] (M = Ca, Sr, Ba) were treated with phosphinoselenoic amine [Ph2P(Se)NH(CHPh2)] (3), prepared by the treatment of bulky phosphinamines [Ph2PNH(CHPh2)] (1) with elemental selenium in THF, and afforded homoleptic alkaline earth metal complexes of composition [M(THF)2{Ph2P(Se)N(CHPh2)}2] (M = Ca (7), Sr (8), Ba (9)). The metal complexes 7–9 can also be obtained via salt metathesis route where the alkali metal phosphinoselenoic amides of composition [{(THF)2M′Ph2P(Se)N(CHPh2)}2] (M′ = Na (5) and K (6)) were reacted with respective metal diiodides in THF at ambient temperature. The solid state structures of the alkali metal complexes 5–6 and alkaline earth metal complexes 7–9 were established by single crystal X-ray diffraction analysis. In the solid state, alkali metal complexes 5 and 6 are dimeric and form a poly-metallacyclic structural motif. In contrast, complexes 7–9 are monomeric and a direct metal–selenium bond is observed in each case.

Highly Active and Iso‐Selective Catalysts for the Ring‐Opening Polymerization of Cyclic Esters using Group 2 Metal Initiators

“…Strong absorption bands for P=S and P=Se bonds appear at 550, 552, and 585 cm −1 (for complexes 3 a , 3 b , and 4 b , respectively) in the FTIR spectra, which are in agreement with reported values . Both complexes 3 b and 4 b show a sharp signal in the 31 P{ 1 H} NMR spectra, δ =52.4 ppm ( 3 b ) and 52.4 ppm ( 4 b ), which are in the same region as that of the free ligand 2 ‐ H2 ( δ =53.8 ppm; Figures FS18, FS21, and FS13 in the Supporting Information).…”

Synthesis and Structure of Potassium and Barium Complexes With Diphenylphosphinothioicamido Ligand Containing Ba-S Direct Bonds

“…The Ba1-O1 (2.737(7) Å) and Ba1-N1 (2.744(7) Å) distances of complex 3 are almost similar to that (2.716(6) and 2.778(6) Å, respectively) of the corresponding values to our previously observed complex [Ba(THF) 2 {Ph 2 P(Se)N(CHPh 2 )} 2 ]. 20 The Ba1-S1 distance 3.179(2) Å is comparable with the Ba-S distance 3.133(2) Å for [Ba(THF) 4 (S-2,4,6-t Bu 3 C 6 H 2 ) 2 ] but slightly shorter than that of 3.396(2)-3.629(2) Å for [Ba(H 2 O) 4 (H 2 2,4,6-S 3 C 3 N 3 ) 2 ] reported by Ruhlandt-Senge and coworkers. 18 Thus the central atom barium adopts a distorted octahedral geometry due to coordination from two 1 moieties and two THF molecules.…”

“…20 In complex 3, the four-membered BaSPN metallacycle is nonplanar and the atoms S1 (0.062 Å and N1 (0.092 Å) are placed above, and P1 atom is placed below (0.110 Å) the weighted least-squares best plane having Ba1, S1, P1, N1 atoms. Complex 3 is another example of barium sulfur complex having a barium sulfur direct contact.…”

“…20 The phosphineamine, A, can coordinate to the metal through the nitrogen atom and phosphorus atom resulting a highly strained three member metallacycle and reported by Roesky and others. [21][22][23][24][25] The phosphineamine chalcogenides, A-NPO, A-NPS, and A-NPSe, can either form a four member metallacycle if the nitrogen and chalcogen atom (O, S, Se) coordinate to the metal center, or it can form two fused three member metallacycle to stabilized the metal complexes and it is observed by us in alkali metal as well as heavier alkaline earth metal complexes.…”

“…[21][22][23][24][25] The phosphineamine chalcogenides, A-NPO, A-NPS, and A-NPSe, can either form a four member metallacycle if the nitrogen and chalcogen atom (O, S, Se) coordinate to the metal center, or it can form two fused three member metallacycle to stabilized the metal complexes and it is observed by us in alkali metal as well as heavier alkaline earth metal complexes. 19,20 Thus, due to the presence of adjacent three potentially donor atoms, polymetallacyclic structural motif of the metal complexes can be observed. …”