Alkali Metal Complexes of a Bis(diphenylphosphino)methane Functionalized Amidinate Ligand: Synthesis and Luminescence

Abstract

A novel bis(diphenylphosphino)methane (DPPM) functionalized amidine ligand (DPPMÀ C(N-Dipp) 2 H) (Dipp = 2,6-diisopropylphenyl) was synthesized. Subsequent deprotonation with suitable alkali metal bases resulted in the corresponding complexes [M{DPPMÀ C(N-Dipp) 2 }(L n )] (M = Li, Na, K, Rb, Cs; L = thf, Et 2 O). The alkali metal complexes form monomeric species in the solid state, exhibiting intramolecular metal-π-interactions. In addition, a caesium derivative [Cs {PPh 2 CH 2 -C(N-Dipp) 2 }] 6 was obtained by cleavage of a diphenylphosphino moiety, forming an unusual six-membered ring structure in the solid state. All complexes were fully characterized by single crystal X-ray diffraction, NMR spectroscopy, IR spectroscopy as well as elemental analysis. Furthermore, the photoluminescent properties of the complexes were thoroughly investigated, revealing differences in emission with regards to the respective alkali metal. Interestingly, the hexanuclear [Cs{PPh 2 CH 2 -C(N-Dipp) 2 }] 6 metallocycle exhibits a blue emission in the solid state, which is significantly red-shifted at low temperatures. The bifunctional design of the ligand, featuring orthogonal donor atoms (N vs. P) and a high steric demand, is highly promising for the construction of advanced metal and main group complexes.

Synthesis and Coordination Behavior of a Hybrid Phosphanylferrocene Amidine Ligand

“…1 H NMR (400 MHz, CD 2 Cl 2 ): δ = 1.26 (d, 3 J HH = 3.5 Hz, 15H, C 5 Me 5 ), 2.92 (br s, 6H, NMe 2 ), 3.41 (br s, 2H, fc), 3.85 (br s, 2H, fc), 4.37 (s, 2H, fc), 4.46 (br s, 2H, fc), 7.36-7.48 (br m, 6H, PPh 2 ), 7.73 (s, 1H, CH=N), 7.90-8.02 (br m, 4H, PPh 2 ) ppm. 13 Synthesis of [RuCl(η 6 -p-cymene)(1-k 2 P,N)][BARF] (8): [RuCl 2 (η 6 -p-cymene)] 2 ] (31 mg, 0.050 mmol) and 1 (44 mg, 0.10 mmol) were mixed in dry chloroform (5 mL), and the resulting solution was stirred at room temperature for 3 h to give compound 6. Next, sodium tetrakis[3,5-bis(trifluoromethyl)phenyl] borate (89 mg, 0.10 mmol) was introduced to the reaction mixture, which was stirred for another hour and filtered through a PTFE syringe filter to remove NaCl.…”

“…Examples of these compounds range from amidine-tagged triphenylphosphane derivatives A [2] (Scheme 1), the related symmetrical P 2 N 2 donor B [3] and its donor-unsymmetric counterpart C [4] to the sterically constrained cyclic compounds D, [5] and compound E functionalized in the meso position. [6] In the chemistry of ferrocene ligands, [7] compounds with amidine donor groups remain scarce, [8] being mainly represented by amidines of type F and G (Scheme 2). These compounds were isolated in their free form or as salts with alkali metal cations and further studied as ligands for transition metal ions and main group elements.…”

“…The structural diversity of amidine and amidinate ligands and complexes thereof can be further enhanced by introducing additional donor groups, as previously demonstrated for hybrid donors in which soft phosphane and the relatively harder amidine moieties were combined. Examples of these compounds range from amidine‐tagged triphenylphosphane derivatives A [2] (Scheme 1), the related symmetrical P 2 N 2 donor B [3] and its donor‐unsymmetric counterpart C [4] to the sterically constrained cyclic compounds D , [5] and compound E functionalized in the meso position [6] …”

Cooperative Effects in Heterometallic Complexes

“…The current special issue of Chemistry -a European Journal issue comprises 23 contributions in total, 17 of which stem from work that was conducted within the framework of the 3MET.de center, [1][2][3][4]6,[8][9][10][11]14,[16][17][18][19][20][21]23] and six from outside. [5,7,12,13,15,22] There are two reviews: one is focused on elucidating the magnetic benefits and challenges of cooperativity within 3d-4f based coordination clusters of archetypical butterfly type, [21] and the other one highlights more generally the advancement of inorganic coordination chemistry by spectroscopy of isolated molecules in view of the applied methods and the achieved applications.…”

“…[5,7,12,13,15,22] There are two reviews: one is focused on elucidating the magnetic benefits and challenges of cooperativity within 3d-4f based coordination clusters of archetypical butterfly type, [21] and the other one highlights more generally the advancement of inorganic coordination chemistry by spectroscopy of isolated molecules in view of the applied methods and the achieved applications. [18] Three communications, [3,12,22] one concept article [8] and 17 full papers [1,2,[4][5][6][7][9][10][11][13][14][15][16][17]19,20,23] document and discuss particular 3MET species and their relevance for our understanding of the TM interactions within. A contribution on the development and application of a complete active space spin-orbit configuration interaction program designed for molecule magnets deserves special mention: this manuscript appears in a more specialized sister journal.…”