Silicon(IV) Chelates of an (ONN')-Tridentate Pyrrole-2-Carbaldimine Ligand: Syntheses, Structures and UV/Vis Properties

Abstract

The tridentate (ONN )-chelator properties of the pyrrole-2-(o-hydroxyphenyl)carbaldimine dianion (L 2− ) were explored for the neutral penta-coordinate diorganosilicon complexes LSiRR (R,R = Ph, Ph; Ph, Me; Ph, tBu) where the ligand L occupies the ax-eq-ax sites in a distorted trigonalbipyramidal arrangement arround the silicon atom, and for the neutral hexa-coordinate L 2 Si, that has a mer-coordination. Single-crystal X-ray diffraction analyses show an almost planar ligand backbone with a Si-N bond to the imine group that is shorter in hexa-coordinate L 2 Si than in pentacoordinate LSiRR . In sharp contrast to the almost colorless neutral ligand LH 2 , both complexes show pronounced UV/Vis absorptions in the red-brown region that originate from HOMO -LUMO and HOMO-1 -LUMO transitions, and that are due to intra-ligand π-π * transitions from the N-ooxyphenylimine towards the imine moiety.

Hydrosilylation in Aryliminopyrrolide‐Substituted Silanes

“…This contrasts with the geometry observed for the monosubstituted compounds 1 a and 1 b , which can be explained by the steric influence of the dipp moieties, which minimize their repulsion with each other and with the pyrrole groups in this geometry. The electron‐withdrawing nature of the pyrrole groups likely allows them to engage in a 3c‐4e bond . In the crystal structure, the molecule is located on an exact crystallographic twofold rotation axis.…”

“…The better part of the existing compounds with an N ‐pyrrolylsilyl substructure is being studied in the form of 1) phthalocyanines, porphyrins, and analogues thereof; 2) silyl‐protected pyrroles (mainly R 3 SiPyr where R=alkyl or aryl); or 3) chemical vapor deposition (CVD) precursors (Pyr n SiH (4− n ) ; n =1–3) . Furthermore, three research groups have specifically studied the structure and reactivity of pyrrolylsilane derivatives (Scheme ): the dihydroxyphenol dipyrrin ( I ) by Sakamoto et al., the (NNO) pyrrolehydroxyphenol carbaldimine ( II ) by Gerlach et al., and dipyrrins ( III ) and acylpyrroles ( IV ) by Kämpfe et al . Interestingly, the latter comment that the acyl moiety in IV does not undergo hydrosilylation; the acylpyrrolide hydrosilanes involved during the preparation of IV preferentially liberate H 2 upon reaction with the second ligand.…”

Hexacoordinate Silicon Compounds with a Dianionic Tetradentate (N,N′,N′,N)-Chelating Ligand

“…Based on our experience with pyrrolide as anionic anchoring group in chelating ligands for Si coordination chemistry [20,64,[82][83][84], we studied the syntheses and molecular structures of silicon compounds with a pyrrole-2-carbaldimine functionalized (N,N 1 ,N 1 ,N)-chelating dianionic tetradentate ligand. This ligand, H 2 L, has already been reported in the literature [85] and was synthesized by condensation of o-phenylenediamine with two equivalents of pyrrole-2-carbaldehyde (Scheme 2).…”

“…Whereas the former preferentially bind to Si atoms that carry strongly electron withdrawing groups (e.g., formation of pyridine adducts of halosilanes, Scheme 1, A, [1][2][3]), the latter offer greater opportunities of creating five-and six-coordinate silicon compounds even in case of the absence of halides from the silicon coordination sphere (e.g., pentacoordinate silicon with SiC 5 coordination sphere, B [4][5][6]; and hexacoordinate silicon with a tetradentate chelator and two Si-CH 3 groups, C [7]). For various reasons, such as activation of Si-X bonds by silicon hypercoordination [8][9][10][11][12][13][14][15][16], exploring special electronic/optical properties arising from the higher coordination number of silicon in combination with selected ligands [17][18][19][20] or the aim of creating and exploring hitherto unusual Si coordination compounds, e.g., with transition metals [21][22][23][24][25][26][27][28][29] or very soft Lewis bases in their ligand sphere [30][31][32][33][34][35][36][37][38], silicon coordination chemistry continues to be an attractive research field, reflected by frequently published research articles [39][40]…”

2‐Acylpyrroles as Mono‐anionic O,N‐Chelating Ligands in Silicon Coordination Chemistry

“…In the course of our investigations, we have studied silicon complexes with bi‐, tri‐, and tetradentate O , N ‐donor ligands,3b,c,f, 4a,b, 6 silicon complexes with five‐membered N ‐heterocyclic donor moieties,2g, h, 7 and other silicon compounds of pyrrole‐derived ligand systems 8. In the work reported herein, we now address silicon complexes with pyrrole‐functionalized bidentate O , N ‐chelating ligands.…”