Reversible intramolecular base-stabilization in silylene (silanediyl) complexes: surprising reactivity for silylene coordination compounds with a dynamic N.cntdot..cntdot..cntdot.Si.cntdot..cntdot..cntdot.N bond

Abstract

The silane [ 2-(MezNCHz)C&] ZSiClz (7) shows a new dynamic N**&-N "flip-flop" coordination mode below T, = 233 K (AG* = 46.5 (f0.5) kJ mol-l) with both amine donors displacing each other. 7 is pentacoordinated in the solid state; crystal data: orthorhombic, Paca, a = 13.802(1) A, b = 17.908(1) A, c = 15.544(2) A, Z = 8. Reaction of the silanes C~H~[~-(M~ZNCHZ)C~H~]S~C~P (61, 7, and [~-( M~Z N C H Z ) -~-(~-C~H~) C~H~~Z S~C~Z (8) with chromiumpentacarbonylmetallate yields the silanediyl complexes [~-(M~zNCHZ)C~H~IC~H~S~=C~(CO)B (111, [2-(Mez-N C H Z ) C~H~] zSi=Cr(CO)5 (12), and 12-(M~zNCHZ)-~-(~-C~H~)C~H~I zSi=Cr(CO)s (13); 12-(Mez-N C H Z ) C~H~] H S~= C~( C O )~ (14) was obtained by photolytic methods. Silanediyl complexes with one chelating donor show a rigid coordination of the donor to silicon which can be lifted at higher temperatures (95 'C for 11, AG* = 80.4 (*0.5) kJ mol-'). A single crystal X-ray structure determination of 11 reveals a CrSi bond distance of 2.409(1) A and a N-Si bond length of 1.991(2) A. Crystal data: triclinic, Pi, a = 9.401(1) A, b = 10.207(1) A, c = 11.586(1) A, Z = 2. Silanediyl complexes with two intramolecular donor functions feature a dynamic "flip-flop" coordination of the amine groups to silicon. Both (dimethy1amino)phenyl groups in 12 and 13 can be detached from silicon under liberation of a three-coordinate silicon atom at T, = 58 'C (VTJH-NMR), AG* = 67.1 (f0.5) kJ mol-l for 12 and T, = 61 'C, AG* = 70.1 (k0.5) kJ mol-' for 13. A single crystal X-ray structure determination of 12 gives 2.408(1) A for the Si-Cr bond length and 2.046(2) A for the N1-Si dative bond (the second contact N2-Si has a nonbonding distance of 3.309 A; the sum of bond angles at silicon amounts to 351.3'). Crystal data: triclinic, Pi, a = 9.531(1) A, b = 10.339(1) A, c = 11.676(1) A, Z = 2. The donor in 12 has been functionalized at the nitrogen atom by protonation or complexation with BF3. Photolysis of 12 and 13 leads to a 1,2-amine shift of one donor from silicon to the metal with loss of CO. The product [2-(Me~NCHz)c6H31 [2-(MezrjCHz)C6H3] Si=Cr(CO)r (20) has been characterized by a single crystal X-ray structure determination and has a bond distance Cr-Si 2.3610(4) A and N1-Si 1.981(1) A. Crystal data: monoclinic, P21/c, a = 10.344(5) A, b = 11.761(3) A, c = 18.96(1) A, Z = 4. Furthermore, the silanediyl complex 12 has been immobilized on silica gel. IR and UV spectroscopy and 13C CPMAS NMR provide evidence for the fixation of (silica-0-) [~-(HNM~zCHZ)C~H~~[~-(M~ZNCHZ)C~H~~ Si=Cr(CO)s (22) to the surface via the silicon atom. Reaction of 13 with HzO leads to (HO) [~-( H N M~z C H Z ) C~H~I [~-( M~Z N C H Z ) C~H~I S~-Cr(CO)5 (23) which has a structure similar to 22 with a Cr-Si bond length of 2.469(2) A. The dimethylamino or dimethylammonium substituent is pointing away from the silicon atom forming hydrogen bridges between Nl-*HO*-HN2; crystal data: monoclinic, P&/n, a = 13.198(2) A, b = 17.017(2) A, c = 17.066(1) A, Z = 4.

Transition Metal Complexes of (Schiff Base)Divalent Group 14 Element Species [(salen)M]n=M′(CO)6–n (n = 1, 2; M = Ge, Sn, Pb; M′ = Cr, W)

“…They were found to be soluble only in polar and protic solvents (THF, CHCl 3 , CH 2 Cl 2 , DMSO, DMF, MeOH). Direct irradiation at room temperature of mixtures of the divalent compounds (salen)M and the hexacarbonyl complexes MЈ(CO) 6 (MЈ ϭ Cr, W) also resulted in the formation of the expected monometal(II) complexes in yields depending on the nature of both the Group 14 atom M and the transition metal MЈ (Scheme 2). With (salen)germylene and -stannylene, the mono compounds 4 and 5 were produced in high yields when the reactions were carried out using Cr(CO) 6 .…”

“…Direct irradiation at room temperature of mixtures of the divalent compounds (salen)M and the hexacarbonyl complexes MЈ(CO) 6 (MЈ ϭ Cr, W) also resulted in the formation of the expected monometal(II) complexes in yields depending on the nature of both the Group 14 atom M and the transition metal MЈ (Scheme 2). With (salen)germylene and -stannylene, the mono compounds 4 and 5 were produced in high yields when the reactions were carried out using Cr(CO) 6 . Using W(CO) 6 under similar reaction conditions, substitution of more than one carbonyl was observed and the disubstituted compounds 10-12 with the ligands in a cis arrangement were formed alongside the monosubstituted species 7-9 (Scheme 2).…”

“…With (salen)germylene and -stannylene, the mono compounds 4 and 5 were produced in high yields when the reactions were carried out using Cr(CO) 6 . Using W(CO) 6 under similar reaction conditions, substitution of more than one carbonyl was observed and the disubstituted compounds 10-12 with the ligands in a cis arrangement were formed alongside the monosubstituted species 7-9 (Scheme 2). Extension of this procedure to the reactions of (salen)plumbylene with Cr(CO) 6 and W(CO) 6 led to complexes 6 in 70% yield and to a mixture of 9 and 12 (30:70, as determined by 1 H-NMR), respectively.…”

“…Using W(CO) 6 under similar reaction conditions, substitution of more than one carbonyl was observed and the disubstituted compounds 10-12 with the ligands in a cis arrangement were formed alongside the monosubstituted species 7-9 (Scheme 2). Extension of this procedure to the reactions of (salen)plumbylene with Cr(CO) 6 and W(CO) 6 led to complexes 6 in 70% yield and to a mixture of 9 and 12 (30:70, as determined by 1 H-NMR), respectively. In contrast, attempts to prepare the (salen)MϭMЈ(CO) 5 (MЈ ϭ Cr, W) complexes simply by heating mixtures of the starting materials at 80°C for 24 h proved unsuccessful.…”

“…[6][7][8][9][10][11][12][13][14] Each of the new complexes has been characterized by 1 Hand 13 C-NMR, and by 119 Sn-NMR in the case of 5, 8, 11, and 14, as well as by IR spectroscopy in all cases. The molecular structures of 5, 8, 11, and 14, determined by X-ray structure analyses, reveal a pentacoordinated tin atom.…”