Diamond electrodes doped with this element may be used in organic electro-synthesis due to their large electrochemical window. Hydroxylation reactions often use a disiamyl-substituted compound of this element. A bulky compound of this element (15[2])and a phosphine form the classic frustrated Lewis pair. A base attacks this element before transmetallating an aryl group onto palladium in the (*) Suzuki coupling. This element (10[1])adds across a double bond, followed by oxidation with a peroxide, (10[1])in an anti-Markovnikov addition of water across a double bond. This element’s trihydride dimerizes (10[1])into a compound with two three-center, two-electron bonds, since this element typically only forms three covalent bonds (10[1])in violation of the octet rule. For 10 points, name this trivalent element whose atomic number is 5. ■END■ (10[1])