11111111111111111 1I111! UIIJ WII mil 1111 EJ52-1995-533 Journal of the Chinese Chemical Society, 1995 t 42,533-535 Synthesis of Heterobimetallic Phosphido-Bridged W·Mo Complexes with Chelating dppe and dppm Ligands Wen-Jm Wu ( Jiun-Yi Hsu ( ), Yuh-Shang Wen ( ) and Shin-Guang Shyu* ( i*WT1t ) Institute of Chemistry, Academia Sinica, Taipei, Taiwan 11529, Republic of China i r Reactions between CpW(COh<I-l-PPh 2)Mo(CO)5 (1) and bidentate phosphines (dppm and dppe) pro- duced complexes CpW\COMI-l-PPh 2) Mo(COMdppm) (2a) and CpW(COMI-l-PPh 2)Mo(COMdppe) (2b) with chelating dppm and dppe ligands as only products. No bridging bidentate phosphine complex was ob- served. Both complexes were spectroscopically characterized. 533 An interesting feature of a bimetallic phosphide- bridged complex is the breakage and formation of the metal- metal bond in the complex during reaction.!" Metal-metal bonds in these complexes may have significant donor-ac- ceptor The breakage and formation of the met- al-metal bond are similar to the reversible coordination of the ligand to the metal such that the metal-metal bond is considered to follow a typical donor-acceptor mode of li- gand-metal hinding with an electron lone pair localized on the ligand. Addition of phosphines to CpW(COh(I-l-- PPh 2)"Mo(COh (1) resulted in breakage of the metal-metal bond in 1 to form CpW(COMI-l-PPh2)Mo(CO)4L (L = P(OMeh. PMe3,PPh2H). Further photolysis or pyrolysis of CpW(COh(Il-PPh,)Mo(COhL led to detachmentof oneCO ligand and regenerated the metal-metal bond to form I I 7 CpW(COh(Il-PPh2)Mo(CO)4L. It is of interest to see whether a bidentate phosphine ligand can coordinate to both metals to produce a heterobimetallic bridging bidentate phosphine complex when it reacts with 1. Here, we report Ute reaction between 1 and bidentate phosphincs, dppm and dppe, and characterization of the products. Reactions between 1 and bidentate phosphines (dppm and dppe) in THF under reflux conditions produced red sol- ids that were characterized as CpW(CO)z(/l-PPh 2)M'0(COh F I (dppm) (2a) and CpW(COMIl-PPh 2)Mo(CO)3(dppe) (2b) respectively as only products. Both complexes were stable at room temperature in air in the solid state. The 31 p NMR spectrum of 2 shows three signals that indicate two phosphorous atoms in the bidentate phosphines to be coordinated to the complexes. Both phosphorus atoms in the ligand are coordinated to Mo instead of forming a bridging bidentate phosphine complex because h.w satel- lites were absent The signals at 137.96 ppm (2a) and 129.40 ppm (2b) are assigned to bridging phosphido phos- phorus atoms because h-w satellites were observed. The low field signal indicates a metal-metal bond in 2. 8 In 2b, a signal at 63.92 ppm is assigned to phosphorus trans to the phosphide bridge in the chelating dppm ligand based on its large J p -p value. A similar argument applies to the assignment of 31p NMR spectrum of 2a. In 2a, the sig- nals of dppm are at relatively upfield positions (5.85 ppm and -14,49 ppm) compared to the corresponding signals of dppe (63.92 ppm and 43.71 ppm) in 2b. The phosphorous atom in a four member ring is expected to have signal at relatively upfield position compared to the signal of the phosphorous atom in a five member ring in J1p NMR spec- tra. 8e Formation of 2 probably proceeded through the inter- mediate CPWCCOMI-l-PPh 2HI1'0(CO)4[PPh2(CH2)xP Ph2] (3a, x = 1; 3b, x =2) as reaction between 1 and PPh3 pro- duced CpVl(COh(Il-PPh2)M'o(COMPPhJ).7 Further substi- tution of one Mo carbonyl ligand in 3 by coordinated biden- tate phosphines resulted in formation of 2 (Scheme 1). In (CO)4Ru(Il-PPh2)C'o(COh, reaction between this complex and dppm resulted in two products, one with a cbelating dppm ligand and the other with a bridging dppm ligand." Reaction between 1 and dppm formed no bridging dppm complex 4 for two possible reasons. One is steric hin- drance of the Cp ring and the bridging drphenylphosphido fragment. According to the structure of 1, the Cp ring occu- pies a position such that steric hindrance between Cp and the phenyl rings is minimized. The coordination of the bulky dppm to both Mo and W to form the bridging biden- tate phosphine complex would generate great steric hin- drance that might prohibit formation of the bridging com- plex. Second, the dppm must occupy a position trans to the phosphide bridge in 3 to minimize steric hindrance as in the case of CpW(CCh(Il-PPh2)Mo(CO).PPh3_? Hence further coordination of a second phosphorus atom in coordinated dppm to the adjacent W becomes difficult. As a result, in or- der to synthesize bridging dppm or dppe heterobimetallic complexes from a heterobimetallic precursor, we must sew