Question

The reaction of diborane in diethyl ether with \(X\) gives metalloborohydride. \(X\) is a

• A. Metal
• B. Metal halide
• C. Metal hydride
• D. Metal oxide

Hint:

Diborane reacts with metal hydrides to form metal borohydrides: \[ MH+B_2H_6 \rightarrow MBH_4 \] Example: \[ NaH+B_2H_6 \rightarrow NaBH_4 \]

Answer 1

The Correct Option is C

Step 1: Recall the structure and reactivity of diborane (B₂H₆).
Diborane (B₂H₆) is an electron-deficient compound with 3-center-2-electron bonds. It reacts readily with nucleophilic reagents including metal hydrides.
Step 2: Identify what a metalloborohydride is.
A metalloborohydride is a salt containing the borohydride anion BH₄^-, for example NaBH₄ (sodium borohydride), LiBH₄ (lithium borohydride). These are vital reducing agents in chemistry.
Step 3: Write the reaction of diborane with a metal hydride.
When diborane reacts with sodium hydride (NaH) in diethyl ether: \[ 2NaH + B_2H_6 \rightarrow 2NaBH_4 \] The hydride ion (H^-) from NaH attacks the electrophilic boron in B₂H₆, forming the tetrahedral BH₄^- ion.
Step 4: Identify X.
X is a metal hydride (such as NaH, LiH). In diethyl ether solvent, metal hydrides react with diborane to produce metalloborohydrides.
Step 5: Explain the mechanism.
The metal hydride provides H^- ions that attack the electron-deficient boron. Since B₂H₆ has only 12 valence electrons (electron-deficient), it readily accepts electron pairs from H^-. Each B accepts 2 additional H^- to form BH₄^-.
Step 6: Conclusion.
X is a metal hydride (e.g., NaH or LiH). The reaction: $2NaH + B_2H_6 \rightarrow 2NaBH_4$ illustrates formation of metalloborohydride in diethyl ether.
\[ \boxed{X = \text{Metal hydride (option 3)}} \]