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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.

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J. L. Word, J. Am. Chem. SOC. 95 (1973) 7878. IS] 3: triclinic crystals; space group Pi (No. 2, centrosymmetric); a=8.6I(7, h= 10.345, c = 16.557 A, a=72.79, p= 103.50, y= 116.33"; Y= 1265 A', pc,,,L,,= 1.251 g cm-', 2 = 4 . L(MoK,,)=0.70926 A. 6356 reflections were measured (0-20 scan mode) of which 4574 with I > 2 a ( l ) were used for the solution by direct methods (MULTAN 78). Further details are available on request from the Director of the Cambridge Crystallographic Data Centre. University Chemical Laboratory, Lensfield Road, Cambridge CB2 IEW (England) by quoting the full literature citation.[6] S. Angew. Chem. lnr. Ed Engl. 26 (1987) No. 7 0 VCH Verlagsgesellschafi mbH, 0-6940 Weinheim. 1987 0570-0833/87/0707-0669 S 02.50/0

The (trichlorosilyl) (and -germyl)metal carbonyls Co(CO) 4 SiCl 3 , Co(CO) 4 GeCl 3 , Mn(CO) 5 -SiCl 3 , and cis-Fe(CO) 4 (SiCl 3 ) 2 have been synthesized in high yields. He I photoelectron spectra (UPS) of the complexes have been measured and interpreted on the basis of empirical arguments and density functional theory (DFT) calculations. For cis/trans-Fe(CO) 4 (SiCl 3 ) 2 isomers the calculations predict the trans-isomer to be more stable than cis by 15.2 kJ mol -1 . The cis-isomer is exclusively present in the solid state and in the gas phase. UPS results suggest the importance of charge polarization effects and the lack of π-back-donation along TM-Si bonds. The calculated M-Si bond distances amounted to 2.34 Å (Co-Si), 2.43 Å (Co-Ge), 2.47 Å (Mn-Si), 2.41 Å (trans-Fe-Si), and 2.45 Å (cis-Fe-Si). For Co(CO) 4 SiCl 3 , the DFT calculated Co-Si bond dissociation energy was 317.7 kJ mol -1 , compared to 222.2 kJ mol -1 for Co-C energy in Co(CO) 4 CCl 3 .