Synthesis and Oligonuclear Structures of Strontium and Barium Complexes with Protonated and Deprotonated N-Mesityl-P,P-diphenylphosphinic Amide Ligands

Abstract

Metalation of N -mesityl- P , P -diphenylphosphinic amide Ph 2 P(O)-NHMes (HL, I ) with MgBu 2 and Ae{N(SiMe 3 ) 2 } 2 (Ae = Ca, Sr, and Ba) yields alkaline-earth metal complexes with the compositions of [(thf) n Ae(L·HL) 2 ] [Ae/n = Mg/0 ( II ), Ca/2 ( III )] as well as of [Sr 2 L 3 (L·HL)(HL)] ( 1 ), [Ba 2 L 3 (L·HL)(HL)] ( 2 ), [Ba 3 L 6 ] ( 3 ), and [(thf) 2 Ba 3 L 6 ] ( 4 ). In III , 1 , 2 , and 3 , the alkaline-earth metal atoms are in severely distorted octahedral environments, and the structural distortions are partially caused by the small O-Ae-N bite angles of the chelating Ph 2 P(O)-NMes anions. The substructures (L·HL) contain N–H···N hydrogen bridges, stabilizing the arrangement of the ligands in complexes II , III , 1 , and 2 . In the trinuclear barium complex [Ba(μ-L) 3 Ba(μ-L) 3 Ba] ( 3 ), a rigid adjustment of the anionic L bases leads to a C 3 -symmetric molecule in the crystalline state with bridging oxygen atoms. Due to the small O–Ba–N bite angles of the chelating anions, vacant coordination sites are available at the outer barium centers. Coordination of thf bases in these gaps yields the complex [(thf)Ba(μ-L) 3 Ba(μ-L) 3 Ba(thf)] ( 4 ). However, THF is unable to deaggregate the trinuclear complexes into smaller barium-containing moieties. Increasing the radius of the alkaline-earth metals and increasing the nuclearity of these compounds lead to decreasing solubility in common organic solvents. NMR studies verify that the molecular structures of these alkaline-earth metal complexes are maintained in ethereal solvents and toluene.

Structural Diversity of Lithium N‐Mesityl‐P,P‐diphenylphosphinimidate of the type [(L)Li{O−PPh2=N−Mes]n Depending on Lewis Base L

“…Molar masses in solution were calculated using the Stalke-ECC-DOSY method (standard: anthracene). [21] The 1 H, 7 Li, 13 C{ 1 H}, and 31 P NMR spectra are depicted in the Supporting Information. Substrates were purchased from abcr, Alfa Aesar, Merck or TCI and used without further purification.…”

“…The yields given are not optimized. 1 H, 7 Li, 13 C { 1 H}, and 31 P NMR spectra were recorded on Bruker Avance III 400 MHz (BBO or BBFO) and Bruker Avance IV (NEO) 500 MHz (Prodigy BBO or Diff50 (DOSY)) spectrometers. Chemical shifts are reported in parts per million relative to SiMe 4 , LiCl and aqueous phosphoric acid as external standards.…”

“…Remarkably, complex 4 has a very distinct pattern with exclusively narrow signals appearing in the 1 H, 31 P and 7 Li NMR spectra despite the fact, that the lithium atoms showed different coordination environments. With the bridging bromide atoms complex 4 has the largest high field shift in the phosphorus and lithium NMR spectra in comparison to the other lithium complexes 1 to 3.…”

“…Addition of dibutylmagnesium or calcium bis[bis(trimethylsilyl)amide] in THF to [Ph 2 P(=O)−N(H)Mes] led to formation of mononuclear [(thf) n Ae{Ph 2 P(=O)−N−Mes} 2 {Ph 2 P(=O)−N(H)−Mes} 2 ] (Ae/n=Mg/0, Ca/2) where only the oxygen bases bonded to the alkaline‐earth metal atoms and peripherical intramolecular N−H⋅⋅⋅N hydrogen bridges stabilized these complexes additionally [6] . In binuclear strontium and barium complexes as well as in a trinuclear barium congener, these anions showed mono‐ and bidentate binding modes even within the same molecule [7] …”

“…[6] In binuclear strontium and barium complexes as well as in a trinuclear barium congener, these anions showed mono-and bidentate binding modes even within the same molecule. [7] Initially, we investigated the possibility to synthesize heterobimetallic organometallics and to simply replace the hydrogen atoms of the NÀ H•••N hydrogen bridges in [(thf) 2 Ae {Ph 2 P(=O)À NÀ Mes} 2 {Ph 2 P(=O)À N(H)À Mes} 2 ] by lithium via metalation of these compounds with n-butyllithium or alternatively via the metathetical approach between magnesium halide and two equivalents of earlier reported [(thf) 2 Li(OÀ PPh 2 =NÀ Mes] 2 . However, heterobimetallic complexes were not accessible by these reactions but during these attempts, new lithium Nmesityl-P,P-diphenylphosphinimidates were discovered and characterized by single crystal X-ray diffractometry.…”