Investigation of photochemical reactions of some metal carbonyls with   methylsalicylaldehydemethanesulfonylhydrazone and 5-methyl-2-hydroxyacetophenonemethanesulfonylhydrazone
Sema Sert1
1 Department of Chemistry, Faculty of Science, Ege University, İzmir, Turkey
e-mail: semasertkimya@hotmail.com

Abstract
Eight new complexes, [M(CO)5(5msalmsh)] [M=Cr;(1a), Mo;(2a); W(3a)], [Re(CO)4Br(5msalmsh)] (4a),  [M(CO)5(5mafmsh)] [M=Cr;(1b), Mo;(2b); W(3b)], [Re(CO)4Br(5mafmsh)] (4b), have been synthesized by the photochemical reaction of the metal carbonyls [M(CO)6] (M= Cr, Mo, W) and          [Re(CO)5Br] with methylsalicylaldehydemethanesulfonylhydrazone (5msalmsh) and 5-methyl-2-hydroxyacetophenonemethanesulfonylhydrazone (5mafmsh). The complexes have been characterized by elemental analysis, LC-MS, FT-IR, 1H NMR spectroscopy. Spectroscopic studies show that  5msalmsh and 5mafmsh behave monodentate ligand and coordinate via an imine N donor atom to the central metal atom in (1a)-(4a) and (1b)-(4b).
Keywords: Hydrazones, monodentate ligands, metal carbonyls, photochemical reactions.

1.Introduction
    Hydrazones possess an important class of biologically active drug molecules.1 It has been synthesized as drugs in order to cure diseases with less toxicity and high effects. Hydrazones having an azometine -NHN=CH- proton are synthesized by heating the appropriate substituted hydrazides with aldehydes in solvents.2,3 Hydrazone compounds are not only intermediates but also very effective organic compounds. Hydrazones are very well-known compounds because of their interesting chemical properties. Hydrazones have enough various biological,4,5 physical6 or industrial7 applications. Hydrazone derivatives with anti-inflammatory,8 analgesic, anticonvulsant, anti-HIV, antimicrobial,9-11 antibacterial,12,13 and antitumor properties14 were reported. Hydrazone derivatives undergoes formation of their transition metals complexes were used in the treatment of tuberculosis.15-17 Characteristic properties of hydrazones are imprinted by the presence of the >C=N-N< structural unit, which contains two nitrogen atoms with nucleophilic character and a carbon which may act as either electrophile or nucleophile according to the reaction environment.18 

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    Sulfonamides/sulfonylhydrazines/sulfonylhyrazones significant pharmacology applications and widespread use in medicine. These compounds have gained importance in bioinorganic and metal based drug chemistry because of their lower cost, lower toxicity and most activity against bacterial diseases.19,20 Moreover, they are used in agriculture field as well as insecticides and herbicides. They are less toxic as compared to other drugs and are scalable.21-23
    In chemical synthesis, photochemical reactions are usually cleaner and more efficient than other types of reactions because the key reagent is light of particular energy. In fine chemical synhhesis and pharmaceutical productions, photochemical reaction steps offer shorter routes for many synthetic schemes, e.g. synthesis of vitamin D. In addition, photocleavage has also become one of the more effective methods for removing protective groups. The use of photochemistry is limited by concerns about scalability, efficiency, and safe operations of the processes.24
    Metal carbonyl complexes are among the most photoreactive transition metal complexes known. The commonly known carbonyls of Cr(0), Mo(0), and W(0) are six-coordinate octahedral complexes, M(CO)6. Other stable complexes containing only the central metal and CO include the dimers M2(CO)102- having a single M-M bond. Numerous compounds of the M(CO)n(L)6-n variety have been prepared, many photochemically.25
    In this work, eight new complexes [M(CO)5(5msalmsh)] [M=Cr;(1a), Mo;(2a); W(3a)], [Re(CO)4Br(5msalmsh)] (4a),  [M(CO)5(5mafmsh)] [M=Cr;(1b), Mo;(2b); W(3b)], [Re(CO)4Br(5mafmsh)] (4b) as shown in Scheme 1 were prepared by the photochemical reactions of [M(CO)6] (Cr, Mo, W) with 5msalmsh and 5mafmsh (shown in Figure 1)  and characterized by elemental analysis, MS, IR and 1H NMR spectroscopy. According to all the spectroscopic data, 5msalmsh and 5mafmsh are monodentate and coordinated via the imine nitrogen donor atom.

                         
Figure 1. The structure of ligands.

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2. Experimental

2.1. Materials and  instrumentation

    Reactions were carried out under a dinitrogen atmosphere using Schlenk techniques. All solvents were dried and degassed prior to use.Elemental analyses were performed using a LECO-CHNS-O-9320 by Technical and Scientific Research Council of Turkey, TUBİTAK. Micro-mass VG Platform-II LC-MS were recorded at TUBİTAK as well. IR spectra were recorded on samples in hexane at Ege University on a Mattson 1000 FT spectrophotometer. 1H NMR spectra were recorded in DMSO-d6  on a 400 MHz High Performance Digital FT-NMR at TUBİTAK.Photochemical reactions were carried out in an immersion-well apparatus by using a medium pressure 400W Mercury lamp .All solvents and silica gel were purchased from Merck. M(CO)6 (M=Cr, Mo, W) and Re(CO)5Br were purchased from Aldrich. These reagents were used as supplied. 5msalmsh and 5mafmsh were prepared by the literature method.26

2.2. Synthesis of metal carbonyl complexes

    Complexes (1a)-(4a) and (1b)-(4b) were prepared by photochemical reactions of metal carbonyls M(CO)6 (M = Cr, Mo, W) and Re(CO)5Br with 5msalmsh and 5mafmsh, and were obtained in 50–70% yields. The methods employed for the preparation of the complexes are very similar, so that the preparation of [Cr(CO)5(5msalmsh)] (1a) is given in detail as a representative example.

2.2.1. [Cr(CO)5(5msalmsh)], (1a). Cr(CO)6 (0.44 g, 2 mmol) and 5msalmsh (0.44 g, 2 mmol) were dissolved in THF (80-100 mL). The solution was irradiated for 2 h at room temperature. During irradiation, the reaction mixture changed from colorless to dark yellow. After dissolving in dichloromethane (10 cm3), petroleum ether (50 cm3) was added, resulting in the precipitation of a dark yellow solid which was washed with petroleum ether and dried under vacuum. Yield (60%). Found (%): C, 38.8; H, 2.5; N, 6.4; S, 7.2. Calcd. for CrC14H12N2SO8 (%): C, 40.0; H, 2.9; N, 6.7; S, 7.6. IR (ʋ, KBr): 2067 (m, CO), 1978 (m, CO), 1950 (s, CO), 1928 (s, CO), 1873 (s, CO), 3158 (s, N-H), 1602(s, C=N), 1315 (s, C-O), 1274 (s, (SO2)as),1152 (s, (SO2)sym) cm-1. 1H NMR (δ, DMSO-d6): 2.10 (s, 3H, CH3-C6H5), 2.94 (s, 3H, CH3-SO2), 6.56-7.20 (m, H, (CH)Ar), 7.95 (s, 1H, HC=N-), 9.98 (s, H, NH), 11.87 (s, 1H, OH). MS(LC,70 eV): m/z (%) = 405 (25) [M+-(Me)], 377 (15) [M+-(Me+CO], 349 (30) [M+-(Me+2CO], 321 (25) [M+-(Me+3CO], 293 (15) [M+-(Me+4CO], 265 (10) [M+-(Me+5CO].

2.2.2. [Mo(CO)5(5msalmsh)], (2a). A similar synthetic procedure as that used for 1a was used expect that Cr(CO)6 was replaced by Mo(CO)6 , giving pale-yellow crystals. Yield (64%).     Found (%): C, 35.6; H, 2.5; N, 5.6; S, 6.5. Calcd. for MoC14H12N2SO8 (%): C, 36.1; H, 2.6; N, 6.0; S, 6.9. IR (ʋ, KBr): 2066 (m, CO), 1990 (m, CO), 1950 (s, CO), 1925 (s, CO), 1871 (s, CO), 3160 (s, N-H), 1602(s, C=N), 1315 (s, C-O), 1274 (s, (SO2)as), 1152 (s, (SO2)sym) cm-1. 1H NMR (δ, DMSO-d6): 2.08 (s, 3H, CH3-C6H5), 2.96 (s, 3H, CH3-SO2), 6.58-7.14 (m, H, (CH)Ar), 7.93 (s,

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1H, HC=N-), 9.96 (s, H, NH), 11.88 (s, 1H, OH). MS (LC,70 eV): m/z (%) = 436 (15) 
[M+-(CO)], 408 (25) [M+-(2CO)], 380 (25) [M+-(3CO)], 352 (15) [M+-(4CO)], 324 (10) [M+-(5CO)].

2.2.3. [W(CO)5(5msalmsh)], (3a). A similar synthetic procedure as that used for 1a was used expect that Cr(CO)6 was replaced by W(CO)6 , giving pale-yellow crystals. Yield (62%). Found (%): C, 29.4; H, 2.0; N, 5.0; S, 5.2. Calcd. for WC14H12N2SO8 (%): C, 30.4; H, 2.2; N, 5.1; S,
5.8. IR (ʋ, KBr): 2065 (m, CO), 1991 (m, CO), 1955 (s, CO), 1922 (s, CO), 1872 (s, CO), 3158
(s, N-H), 1602(s, C=N), 1315 (s, C-O), 1274 (s, (SO2)as), 1152 (s, (SO2)sym) cm-1. 1H NMR (δ,DMSO-d6): 2.14 (s, 3H, CH3-C6H5), 2.92 (s, 3H, CH3-SO2), 6.58-7.14 (m, H, (CH)Ar), 7.94
(s, 1H, HC=N-), 9.94 (s, H, NH), 11.85 (s, 1H, OH). MS (LC,70 eV): m/z (%) = 537 (15) [M+-
(Me)], 509 (10) [M+-(Me+CO], 481 (10) [M+-(Me+2CO], 453 (20) [M+-(Me+3CO], 397 (15) [M+-(Me+5CO].

2.2.4. [Re(CO)4Br(5msalmsh], (4a). A similar synthetic procedure as that used for 1a was used expect that Cr(CO)6 was replaced by Re(CO)5Br , giving pale-yellow crystals. Yield (58%). Found(%): C, 25.4; H, 21.8; N, 4.2; S, 5.1. Calcd. for ReC13H12N2SO7Br (%): C, 25.7; H, 2.0; N, 4.6; S, 5.3. IR (ʋ, KBr): 2112 (w, CO), 2016 (m, CO), 1965 (m, CO), 1932 (s, CO), 3158 (s, N-H), 1602(s, C=N), 1315 (s, C-O), 1274 (s, (SO2)as), 1152 (s, (SO2)sym) cm-1. 1H NMR (δ, DMSO-d6): 2.12 (s, 3H, CH3-C6H5), 2.90 (s, 3H, CH3-SO2), 6.56-7.12 (m, H, (CH)Ar), 7.92 (s, 1H, HC=N-), 9.96 (s, H, NH), 11.86 (s, 1H, OH). MS (LC,70 eV): m/z (%) =  578 (15) [M+-(CO)], 550 (15) [M+-(2CO)], 494 (20) [M+-(4CO)].

2.2.5. [Cr(CO)5(5mafmsh)], (1b). A similar synthetic procedure as that used for 1a was used expect that 5msalmsh was replaced by 5mafmsh, giving pale-yellow crystals. Yield (62%). Found(%): C, 41.2; H, 2.9; N, 6.0; S, 7.0. Calcd. for CrC15H14N2SO8 (%): C, 41.5; H, 3.2; N, 6.4; S, 7.4. IR (ʋ, KBr): 2071 (m, CO), 1970 (m, CO), 1946 (s, CO), 1936 (s, CO), 1872 (m, CO), 3204 (s, N-H), 1608 (m, C=N), 1323 (s, C-O), 1254 (s, (SO2)as), 1150 (s, (SO2)sym) cm-1. 1H NMR (δ, DMSO-d6): 2.20 (s, 3H, CH3-C6H5), 2.98 (s, 3H, CH3-SO2), 6.76-7.28 (m, H, (CH)Ar), 2.20 (s, 3H, CH3-C=N-), 10.86 (s, H, NH), 11.50 (s, 1H, OH). MS (LC,70 eV): m/z (%) = 433 (10) [M+-(3H)], 418 (15) [M+-(3H+Me)], 390 (15) [M+-(3H+Me+CO)], 362 (20) [M+-(3H+Me+2CO)], 334 (15) [M+-(3H+Me+3CO)], 306 (10) [M+-(3H+Me+4CO)], 278 (15) [M+-(3H+Me+5CO)].

2.2.6. [Mo(CO)5(5mafmsh)], (2b). A similar synthetic procedure as that used for 2a was used expect that 5msalmsh was replaced by 5mafmsh, giving pale-yellow crystals. Yield (66%). Found(%): C, 36.8; H, 2.7; N, 5.4; S, 6.2. Calcd. for MoC15H14N2SO8 (%): C, 37.6; H, 2.9; N, 5.8; S, 6.7. IR (ʋ, KBr): 2070 (m, CO), 1971 (m, CO), 1944 (s, CO), 1925 (s, CO), 1872 (m, CO), 3203 (s, N-H), 1608 (m, C=N), 1323 (s, C-O), 1252 (s, (SO2)as), 1152 (s, (SO2)sym) cm-1. 1H NMR (δ, DMSO-d6): 2.18 (s, 3H, CH3-C6H5), 3.02 (s, 3H, CH3-SO2), 6.77-7.20 (m, H, (CH)Ar), 2.24 (s, 3H, CH3-C=N-), 10.87 (s, H, NH), 11.58 (s, 1H, OH). MS (LC,70 eV): m/z (%) = 420 (20) [M+-(2Me+CO], 492 (15) [M+-(2Me+2CO],  364 (15) [M+-(2Me+3CO],  336 (25) [M+-(2Me+4CO],  308 (20) [M+-(2Me+5CO].

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2.2.7. [W(CO)5(5mafmsh)], (3b). A similar synthetic procedure as that used for 3a was used expect that 5msalmsh was replaced by 5mafmsh, giving pale-yellow crystals. Yield (64%). Found(%): C, 31.2; H, 2.3; N, 4.4; S, 5.2. Calcd. for WC15H14N2SO8 (%): C, 31.8; H, 2.5; N, 4.9; S, 5.6. IR (ʋ, KBr): 2064 (m, CO), 1972 (m, CO), 1932 (s, CO), 1921 (s, CO), 1875 (m, CO), 3204 (s, N-H), 1609 (m, C=N), 1324 (s, C-O), 1253 (s, (SO2)as), 1150 (s, (SO2)sym) cm-1. 1H NMR (δ, DMSO-d6): 2.22 (s, 3H, CH3-C6H5), 3.01 (s, 3H, CH3-SO2), 6.75-7.28 (m, H, (CH)Ar), 2.22 (s, 3H, CH3-C=N-), 10.88 (s, H, NH), 11.56 (s, 1H, OH). MS (LC,70 eV): m/z (%) = 551 (10) [M+-(Me)], 523 (10) [M+-(Me+CO], 495 (15) [M+-(Me+2CO],  467 (20) [M+-(Me+3CO],  439 (25) [M+-(Me+4CO],  411 (10) [M+-(Me+5CO].

2.2.4. [Re(CO)4Br(5mafmsh], (4b). A similar synthetic procedure as that used for 4a was used expect that 5msalmsh was replaced by 5mafmsh, giving pale-yellow crystals. Yield (60%). Found(%): C, 26.8; H, 2.0; N, 4.0; S, 5.0. Calcd. for ReC14H14N2SO7Br (%): C, 27.1; H, 2.2; N, 4.5; S, 5.2. IR (ʋ, KBr): 2113 (w, CO), 2022 (m, CO), 1920 (m, CO), 1908 (s, CO), 3204 (s, N-H), 1610(s, C=N), 1324 (s, C-O), 1253 (s, (SO2)as), 1152 (s, (SO2)sym) cm-1. 1H NMR (δ,
DMSO-d6): 2.16 (s, 3H, CH3-C6H5), 2.96 (s, 3H, CH3-SO2), 6.76-7.25 (m, H, (CH)Ar), 2.28 (s, 1H, CH3-C=N-), 10.84 (s, H, NH), 11.58 (s, 1H, OH). MS (LC,70 eV): m/z (%) = 617 (20) [M+-(3H)], 602(10)[M+-(3H+Me)], 546 (25) [M+-(3H+Me+2CO)], 518 (25) [M+-(3H+Me+3CO)], 490 (15) [M+-(3H+Me+4CO)].

3. Results and Discussion

    Complexes (1a-4a) and (1b-4b) were prepared by a photochemical reaction as shown in Scheme 1. The photogeneration of M(CO)5 from M(CO)6 (M=Cr, Mo,W) has been extensively studied. The 16-electron M(CO)5 fragments react quickly with any available donor atom to form a M(CO)5L species. If  L is a bidentate ligand, M(CO)4L chelate or bridging    M2(CO)10(µ-L) compounds may occur.27-29 In this study, photochemical reactions of M(CO)6 (M=Cr, Mo, W), and Re(CO)5Br with 5msalmsh and 5mafmsh ligands proceed in this expected manner and give a series of complexes (1a-4a) and (1b-4b).

    The strong bands at 1618 cm-1and 1628 cm-1 are assigned to ʋ(C=N) stretching mode of the imine group for 5msalmsh and 5mafmsh.These bands are shifted to lower wave number in all complexes. These shifts have been explained as a weekining of the CN bond resulting from the nitrogen to the metal atom.30 No shifting upon complex formation was observed for the ʋas(SO2), ʋsym(SO2), ʋ(NH) and ʋ(CO) stretching vibrations indicating that SO2, NH and CO groups were not coordinated to metal atom in (1a-4b) and (1b-4b). The OH stretching vibration was not both free ligand and in (1a-4a) and (1b-4b) because of hydrogen bonding with the imine nitrogen atom.31

    According to number of carbonyl bands, provides important clues to the environment of the metal centers.32 Five carbonyl stretching bands in (1a-3a) and (1b-3b) are attributed to local C4v symmetry M(CO)5.27,28 Similarly four CO stretching absorptions in (4a,4b) indicate to local C2v symmetry33 (shown in Figure 1). The ʋ(CO) modes in (1a-4a) and (1b-4b) move also to lower wave numbers when compared with the starting carbonyl complexes.27,28

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    In the 1H NMR spectra of (1a-4a) and (1b-4b), the signal for the NH hydrogen of free ligands remain unchanged. No shift of hydroxyl protons with complex formation shows that OH group  does not coordinate to metal atoms. The signals of the HC=N and CH3=N protons  show a small upfield shift, which may be related to changing π-electron density in the C=N bond complex formation in (1a-4a) and (1b-4b). According to these data, 5msalmsh and 5mafmsh behave as monodentate ligands via the imine N donor atom in (1a-4a) and (1b-4b).

    The mass spectra show fragmentation via successive loss of CO groups and fragmentation of the organic ligands.

Scheme 1. The photochemical reaction of M(C0)6 (M=Cr, Mo, W) and Re(CO)5Br with the 5msalmsh and 5mafmsh ligands.

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4. Conclusions
    Eight new metal carbonyl complexes, [M(CO)5(5msalmsh)] [M=Cr;(1a), Mo;(2a); W(3a)], [Re(CO)4Br(5msalmsh)] (4a),  [M(CO)5(5mafmsh)] [M=Cr;(1b), Mo;(2b); W(3b)], [Re(CO)4Br(5mafmsh)] (4b), have been characterized using elemental analysis, 1H NMR, LC-MS and IR spectra. 5msalmsh and 5mafmsh behave as monodentate ligands via the N imine donor atom in (1a-4a) and (1b-4b). IR and NMR spectra of the compounds show that the 5msalmsh and 5mafmsh ligands coordinate to the metal atom for compounds (1a-4a) and (1b-4b) only via an imine N donor atom behaving as a monodentate neutral ligand.26
Acknowledgments
    We thank BP (Turkey) for the provision of the photochemical apparatus and the ResearchFoundation of Ege University for funds and TUBITAK for allocation of time at the NMR, Mass Spectra and Elemental Analyses.

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