This thesis describes the synthesis and characterisation of some new organometallic compounds of manganese, rhenium and boron, with the emphasis on attempts to develop new aspects of boron chemistry. Chapter 1 is written as an introduction to the topics of arachno-metallatetraboranes, and the co-ordination chemistry of unsaturated boron containing heterocycles, and Mn and Re(I) carbonyl derivatives. Chapter 2 is concerned with the synthesis of a series of new [MBr(C0)3L2] {M = Mn and Re, L = P(C6RiCl-4)3, P(C6H40Me-4)3, P(CH2Ph)3, 1/2dppp, 1/2dppb; M = Mn, L = l/2dppfc} and previously reported {M = Mn and Re, L = PPh3, l/2dppm, 1/2dppe; M= Re, L = l/2dppfc }organometallic derivatives. These complexes were characterised by spectroscopic (31P-NMR, IR) and single-crystal X-ray diffraction methods {M = Mn, L = P(C6fuCl-4)3, 1/2dppe, 1/2dppfc; M = Re, L = P(CH2Ph)3, P(C6H40Me-4)3, 1/2dppfc}. The Mn(I) derivatives of monodentate ligands were mer,trans-isomers whereas as all other derivatives werefac,cis-isomers. Chapter 3 repmts the reactions of the complexes described in Chapter 2 with [NBu4] [B3H8] and the synthesis and characterisation of several arachno-2-metallatetraborane derivatives: [M(C0)2Li(B3H8)] (M = Re, L = PPh3, P(C6H4Cl-4)3, P(C6H40Me-4h, P(CH2Ph)3 ; M = Mn and Re, L = l/2dppm, l/2dppp, l/2dppb, l/2dppfc; M = Mn, L = 1/2dppe). Of these derivatives only [Mn(C0)2(dppe)(B3H8) ] has been ~reviously reported. All arachno-2-metallatetraboranes were characterised by NMR (1 B, 31P, 1H) and IR spectroscopy and [Mn(C0)2(dppe)(B3Hs)] and [Re(C0)2(dppfc)(B3H8)] were further characterised by single-crystal X-ray diffraction studies. Chapter 4 describes the synthesis of a series of 1: 1 adducts of the Lewis acid B(C6F5)3 with phosphoryl Lewis bases {Et3PO, 0Pr3PO, 00ct3PO, Ph3PO, (Me0)3PO, (Et0)3PO, (Ph0)3PO, (Et0)2PHO, (nBu0)2PHO, (PhO)iPHO, (Me0)2MePO, (Et0)2MePO, (Et0)2PhPO, (MeO)Me2PO, (EtO)Me2PO} and their subsequent characterisation by spectroscopic (1H, 13C, 19F, 31P -NMR, IR) and single-crystal diffraction studies (Et3PO, Ph3PO). The Lewis acidity of B(C6Fsh has been measured by Gutmann's NMR and Lappert's IR methods, and the synthesis and characterisation of B(C6FshEt0Ac is also reported. Chapter 5 reports the synthesis and a determination of the Lewis acidity of a number of previously reported ArBBr2 compounds (Ar = Ph, 2-MeC5H4, 3-MeC6H4, 4-MeC6H4, 4-EtC6H4, 3,5-Me2C6H3) and unsuccessful attempts to prepare unsaturated 4-membered ring and 6-membered ring B-P heterocyclic compounds by reactions of ArBBr2 (Ar = Ph, 4-MeC6H4) with Li[P(SiMe3)2] or by thermolysis of preformed ArBBr2·PhPH2 adducts. Chapter 6 describes full experimental details of the reactions detailed in Chapters 2 to 5 with crystallographic data for all compounds which were characterised by single-crystal X-ray diffraction methods given in the appendices.