Investigations of the Nature of Zn^II−Si^II Bonds

Abstract

A series of zinc(II) silylenes was prepared by using the silylene {PhC(NtBu)2 }(C5 Me5 )Si. Whereas reaction of the silylene with ZnX2 (X=Cl, I) gave the halide-bridged dimers [{PhC(NtBu)2 }(C5 Me5 )SiZnX(μ-X)]2 , with ZnR2 (R=Ph, Et, C6 F5 ) as reagent the monomers [{PhC(NtBu)2 }(C5 Me5 )SiZnR2 ] were obtained. The stability of the complexes and the Zn-Si bond lengths clearly depend on the substitution pattern of the zinc atom. Electron-withdrawing groups stabilize these adducts, whereas electron-donating groups destabilize them. This could be rationalized by quantum chemical calculations. Two different bonding modes in these molecules were identified, which are responsible for the differences in reactivity: 1) strong polar Zn-Si single bonds with short Zn-Si distances, Zn-Si force constants close to that of a classical single bond, and strong binding energy (ca. 2.39 Å, 1.33 mdyn Å(-1) , and 200 kJ mol(-1) ), which suggest an ion pair consisting of a silyl cation with a Zn-Si single bond; 2) relatively weak donor-acceptor Zn-Si bonds with long Zn-Si distances, low Zn-Si force constants, and weak binding energy (ca. 2.49 Å, 0.89 mdyn Å(-1) , and 115 kJ mol(-1) ), which can be interpreted as a silylene-zinc adduct.

A cyclopentadienyl functionalized silylene – a flexible ligand for Si- and C-coordination

“…6,[20][21][22][23][24][25] We recently presented a pentamethylcyclopentadienyl (Cp*) substituted version [{PhC(NtBu) 2 } Si(C 5 Me 5 )] (Scheme 1) and explored its coordination behavior towards transition metals and its reactivity with chalcogens. [26][27][28] In these complexes, we always observed a 1,2-silicon shi of the silylene on the Cp*-ring.…”

“…Furthermore, due to its relatively high steric demand, the 1,2-silicon shi should be suppressed. [26][27][28][29] [{PhC(NtBu) 2 }Si(C 5 Me 4 H)] (1) was synthesized in a rational approach from [{PhC(NtBu) 2 }SiCl] and KCp 4 in good yields (89%, Scheme 2). In contrast to its analogue, Cp* substituted compound 1 is soluble in all common but halogenfree solvents.…”

“…The resulting silyl anion is bound to the [ZnCp*] fragment, with a short Zn-Si bond distance of 2.3105(11)Å. 26,27,41 Additionally this is one of very few examples of a [ZnR] + -fragment bound directly to a silicon atom. 42,43 Due to the rearrangement and deprotonation the coordination of the silyl anion is different from that of typical silylene zinc species, which feature a dative bond between zinc complexes ZnR 2 and silylene.…”

(2-Pyridyloxy)silanes as Ligands in Transition Metal Coordination Chemistry

“…In some of our studies, we have also shown that late transition metals (Ni(II), Pd(II), and Pt(II)) may serve the role of a lone pair donor at hexacoordinate silicon, for example, in I and II (Chart 1) [5][6][7][8]. That kind of complexes with silicon as a lone pair acceptor in the coordination sphere of a transition metal (TM) thus complements TM silicon complexes with, e.g., silylene ligands, in which the Si atom is the formal lone pair donor, such as III, IV, and V [9][10][11][12][13], and the silyl complexes, in which the TM-Si bond is one out of four bonds to a tetravalent Si atom (e.g., VI, VII, VIII, and IX) [14][15][16][17][18]. In complex IX and some other compounds with group 9 metals [19][20][21][22], the 2-pyridyloxy (pyO) ligand was successfully utilized for stabilizing the TM-Si bond by forming two bridges over the heterodinuclear core.…”

“…In both cases, the Si atom is located on a crystallographically imposed center of inversion, and therefore the asymmetric unit consists of a half molecule and the symmetry related sites (e.g., O1 and O1* at Si1) are trans to each other. Selected bond lengths (Å) and angles (deg) for 5 are as follows: Pd1-Cl1 2.290(1), Pd1-Cl2 2.303(1), Pd1-N1 2.028(2), Pd1-N2 2.036(2), Si1-O1 1.794(2), Si1-O2 1.760(2), Si1-O3 1.770(2), N1-Pd1-Cl1 175.93(7), N2-Pd1-Cl2 176.15(7), Cl1-Pd1-Cl2 91.60(3), Cl1-Pd1-N2 88.91(7), Cl2-Pd1-N1 87.65(7), and N1-Pd1-N2 92.10(9); for 6: Cu1-Cl1 2.238(1), Cu1-Cl2 2.256(2), Cu1-N1 2.008(4), Cu1-N2 1.990(4), Si1-O1 1.790(3), Si1-O2 1.770(3), Si1-O3 1.755(3), N1-Cu1-Cl1 153.97(12), N2-Cu1-Cl2 162.50(12), Cl1-Cu1-Cl2 93.69(5), Cl1-Cu1-N2 90.82(11), Cl2-Cu1-N1 90.31(12), and N1-Cu1-N2 93.03(16).…”